two version of R2R are here HEAD master

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diff --git a/.venv/lib/python3.12/site-packages/xlsxwriter/chart.py b/.venv/lib/python3.12/site-packages/xlsxwriter/chart.py
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+###############################################################################
+#
+# Chart - A class for writing the Excel XLSX Worksheet file.
+#
+# SPDX-License-Identifier: BSD-2-Clause
+#
+# Copyright (c) 2013-2025, John McNamara, jmcnamara@cpan.org
+#
+
+import copy
+import re
+from warnings import warn
+
+from . import xmlwriter
+from .shape import Shape
+from .utility import (
+    _datetime_to_excel_datetime,
+    _get_rgb_color,
+    _supported_datetime,
+    quote_sheetname,
+    xl_range_formula,
+    xl_rowcol_to_cell,
+)
+
+
+class Chart(xmlwriter.XMLwriter):
+    """
+    A class for writing the Excel XLSX Chart file.
+
+
+    """
+
+    ###########################################################################
+    #
+    # Public API.
+    #
+    ###########################################################################
+
+    def __init__(self):
+        """
+        Constructor.
+
+        """
+
+        super().__init__()
+
+        self.subtype = None
+        self.sheet_type = 0x0200
+        self.orientation = 0x0
+        self.series = []
+        self.embedded = 0
+        self.id = -1
+        self.series_index = 0
+        self.style_id = 2
+        self.axis_ids = []
+        self.axis2_ids = []
+        self.cat_has_num_fmt = 0
+        self.requires_category = False
+        self.legend = {}
+        self.cat_axis_position = "b"
+        self.val_axis_position = "l"
+        self.formula_ids = {}
+        self.formula_data = []
+        self.horiz_cat_axis = 0
+        self.horiz_val_axis = 1
+        self.protection = 0
+        self.chartarea = {}
+        self.plotarea = {}
+        self.x_axis = {}
+        self.y_axis = {}
+        self.y2_axis = {}
+        self.x2_axis = {}
+        self.chart_name = ""
+        self.show_blanks = "gap"
+        self.show_na_as_empty = False
+        self.show_hidden = False
+        self.show_crosses = True
+        self.width = 480
+        self.height = 288
+        self.x_scale = 1
+        self.y_scale = 1
+        self.x_offset = 0
+        self.y_offset = 0
+        self.table = None
+        self.cross_between = "between"
+        self.default_marker = None
+        self.series_gap_1 = None
+        self.series_gap_2 = None
+        self.series_overlap_1 = None
+        self.series_overlap_2 = None
+        self.drop_lines = None
+        self.hi_low_lines = None
+        self.up_down_bars = None
+        self.smooth_allowed = False
+        self.title_font = None
+        self.title_name = None
+        self.title_formula = None
+        self.title_data_id = None
+        self.title_layout = None
+        self.title_overlay = None
+        self.title_none = False
+        self.date_category = False
+        self.date_1904 = False
+        self.remove_timezone = False
+        self.label_positions = {}
+        self.label_position_default = ""
+        self.already_inserted = False
+        self.combined = None
+        self.is_secondary = False
+        self.warn_sheetname = True
+        self._set_default_properties()
+        self.fill = {}
+
+    def add_series(self, options=None):
+        """
+        Add a data series to a chart.
+
+        Args:
+            options:  A dictionary of chart series options.
+
+        Returns:
+            Nothing.
+
+        """
+        # Add a series and it's properties to a chart.
+        if options is None:
+            options = {}
+
+        # Check that the required input has been specified.
+        if "values" not in options:
+            warn("Must specify 'values' in add_series()")
+            return
+
+        if self.requires_category and "categories" not in options:
+            warn("Must specify 'categories' in add_series() for this chart type")
+            return
+
+        if len(self.series) == 255:
+            warn(
+                "The maximum number of series that can be added to an "
+                "Excel Chart is 255"
+            )
+            return
+
+        # Convert list into a formula string.
+        values = self._list_to_formula(options.get("values"))
+        categories = self._list_to_formula(options.get("categories"))
+
+        # Switch name and name_formula parameters if required.
+        name, name_formula = self._process_names(
+            options.get("name"), options.get("name_formula")
+        )
+
+        # Get an id for the data equivalent to the range formula.
+        cat_id = self._get_data_id(categories, options.get("categories_data"))
+        val_id = self._get_data_id(values, options.get("values_data"))
+        name_id = self._get_data_id(name_formula, options.get("name_data"))
+
+        # Set the line properties for the series.
+        line = Shape._get_line_properties(options.get("line"))
+
+        # Allow 'border' as a synonym for 'line' in bar/column style charts.
+        if options.get("border"):
+            line = Shape._get_line_properties(options["border"])
+
+        # Set the fill properties for the series.
+        fill = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        # Set the marker properties for the series.
+        marker = self._get_marker_properties(options.get("marker"))
+
+        # Set the trendline properties for the series.
+        trendline = self._get_trendline_properties(options.get("trendline"))
+
+        # Set the line smooth property for the series.
+        smooth = options.get("smooth")
+
+        # Set the error bars properties for the series.
+        y_error_bars = self._get_error_bars_props(options.get("y_error_bars"))
+        x_error_bars = self._get_error_bars_props(options.get("x_error_bars"))
+
+        error_bars = {"x_error_bars": x_error_bars, "y_error_bars": y_error_bars}
+
+        # Set the point properties for the series.
+        points = self._get_points_properties(options.get("points"))
+
+        # Set the labels properties for the series.
+        labels = self._get_labels_properties(options.get("data_labels"))
+
+        # Set the "invert if negative" fill property.
+        invert_if_neg = options.get("invert_if_negative", False)
+        inverted_color = options.get("invert_if_negative_color", False)
+
+        # Set the secondary axis properties.
+        x2_axis = options.get("x2_axis")
+        y2_axis = options.get("y2_axis")
+
+        # Store secondary status for combined charts.
+        if x2_axis or y2_axis:
+            self.is_secondary = True
+
+        # Set the gap for Bar/Column charts.
+        if options.get("gap") is not None:
+            if y2_axis:
+                self.series_gap_2 = options["gap"]
+            else:
+                self.series_gap_1 = options["gap"]
+
+        # Set the overlap for Bar/Column charts.
+        if options.get("overlap"):
+            if y2_axis:
+                self.series_overlap_2 = options["overlap"]
+            else:
+                self.series_overlap_1 = options["overlap"]
+
+        # Add the user supplied data to the internal structures.
+        series = {
+            "values": values,
+            "categories": categories,
+            "name": name,
+            "name_formula": name_formula,
+            "name_id": name_id,
+            "val_data_id": val_id,
+            "cat_data_id": cat_id,
+            "line": line,
+            "fill": fill,
+            "pattern": pattern,
+            "gradient": gradient,
+            "marker": marker,
+            "trendline": trendline,
+            "labels": labels,
+            "invert_if_neg": invert_if_neg,
+            "inverted_color": inverted_color,
+            "x2_axis": x2_axis,
+            "y2_axis": y2_axis,
+            "points": points,
+            "error_bars": error_bars,
+            "smooth": smooth,
+        }
+
+        self.series.append(series)
+
+    def set_x_axis(self, options):
+        """
+        Set the chart X axis options.
+
+        Args:
+            options:  A dictionary of axis options.
+
+        Returns:
+            Nothing.
+
+        """
+        axis = self._convert_axis_args(self.x_axis, options)
+
+        self.x_axis = axis
+
+    def set_y_axis(self, options):
+        """
+        Set the chart Y axis options.
+
+        Args:
+            options: A dictionary of axis options.
+
+        Returns:
+            Nothing.
+
+        """
+        axis = self._convert_axis_args(self.y_axis, options)
+
+        self.y_axis = axis
+
+    def set_x2_axis(self, options):
+        """
+        Set the chart secondary X axis options.
+
+        Args:
+            options: A dictionary of axis options.
+
+        Returns:
+            Nothing.
+
+        """
+        axis = self._convert_axis_args(self.x2_axis, options)
+
+        self.x2_axis = axis
+
+    def set_y2_axis(self, options):
+        """
+        Set the chart secondary Y axis options.
+
+        Args:
+            options: A dictionary of axis options.
+
+        Returns:
+            Nothing.
+
+        """
+        axis = self._convert_axis_args(self.y2_axis, options)
+
+        self.y2_axis = axis
+
+    def set_title(self, options=None):
+        """
+        Set the chart title options.
+
+        Args:
+            options: A dictionary of chart title options.
+
+        Returns:
+            Nothing.
+
+        """
+        if options is None:
+            options = {}
+
+        name, name_formula = self._process_names(
+            options.get("name"), options.get("name_formula")
+        )
+
+        data_id = self._get_data_id(name_formula, options.get("data"))
+
+        self.title_name = name
+        self.title_formula = name_formula
+        self.title_data_id = data_id
+
+        # Set the font properties if present.
+        self.title_font = self._convert_font_args(options.get("name_font"))
+
+        # Set the axis name layout.
+        self.title_layout = self._get_layout_properties(options.get("layout"), True)
+        # Set the title overlay option.
+        self.title_overlay = options.get("overlay")
+
+        # Set the automatic title option.
+        self.title_none = options.get("none")
+
+    def set_legend(self, options):
+        """
+        Set the chart legend options.
+
+        Args:
+            options: A dictionary of chart legend options.
+
+        Returns:
+            Nothing.
+        """
+        # Convert the user defined properties to internal properties.
+        self.legend = self._get_legend_properties(options)
+
+    def set_plotarea(self, options):
+        """
+        Set the chart plot area options.
+
+        Args:
+            options: A dictionary of chart plot area options.
+
+        Returns:
+            Nothing.
+        """
+        # Convert the user defined properties to internal properties.
+        self.plotarea = self._get_area_properties(options)
+
+    def set_chartarea(self, options):
+        """
+        Set the chart area options.
+
+        Args:
+            options: A dictionary of chart area options.
+
+        Returns:
+            Nothing.
+        """
+        # Convert the user defined properties to internal properties.
+        self.chartarea = self._get_area_properties(options)
+
+    def set_style(self, style_id):
+        """
+        Set the chart style type.
+
+        Args:
+            style_id: An int representing the chart style.
+
+        Returns:
+            Nothing.
+        """
+        # Set one of the 48 built-in Excel chart styles. The default is 2.
+        if style_id is None:
+            style_id = 2
+
+        if style_id < 1 or style_id > 48:
+            style_id = 2
+
+        self.style_id = style_id
+
+    def show_blanks_as(self, option):
+        """
+        Set the option for displaying blank data in a chart.
+
+        Args:
+            option: A string representing the display option.
+
+        Returns:
+            Nothing.
+        """
+        if not option:
+            return
+
+        valid_options = {
+            "gap": 1,
+            "zero": 1,
+            "span": 1,
+        }
+
+        if option not in valid_options:
+            warn(f"Unknown show_blanks_as() option '{option}'")
+            return
+
+        self.show_blanks = option
+
+    def show_na_as_empty_cell(self):
+        """
+        Display ``#N/A`` on charts as blank/empty cells.
+
+        Args:
+            None.
+
+        Returns:
+            Nothing.
+        """
+        self.show_na_as_empty = True
+
+    def show_hidden_data(self):
+        """
+        Display data on charts from hidden rows or columns.
+
+        Args:
+            None.
+
+        Returns:
+            Nothing.
+        """
+        self.show_hidden = True
+
+    def set_size(self, options=None):
+        """
+        Set size or scale of the chart.
+
+        Args:
+            options: A dictionary of chart size options.
+
+        Returns:
+            Nothing.
+        """
+        if options is None:
+            options = {}
+
+        # Set dimensions or scale for the chart.
+        self.width = options.get("width", self.width)
+        self.height = options.get("height", self.height)
+        self.x_scale = options.get("x_scale", 1)
+        self.y_scale = options.get("y_scale", 1)
+        self.x_offset = options.get("x_offset", 0)
+        self.y_offset = options.get("y_offset", 0)
+
+    def set_table(self, options=None):
+        """
+        Set properties for an axis data table.
+
+        Args:
+            options: A dictionary of axis table options.
+
+        Returns:
+            Nothing.
+
+        """
+        if options is None:
+            options = {}
+
+        table = {}
+
+        table["horizontal"] = options.get("horizontal", 1)
+        table["vertical"] = options.get("vertical", 1)
+        table["outline"] = options.get("outline", 1)
+        table["show_keys"] = options.get("show_keys", 0)
+        table["font"] = self._convert_font_args(options.get("font"))
+
+        self.table = table
+
+    def set_up_down_bars(self, options=None):
+        """
+        Set properties for the chart up-down bars.
+
+        Args:
+            options: A dictionary of options.
+
+        Returns:
+            Nothing.
+
+        """
+        if options is None:
+            options = {}
+
+        # Defaults.
+        up_line = None
+        up_fill = None
+        down_line = None
+        down_fill = None
+
+        # Set properties for 'up' bar.
+        if options.get("up"):
+            if "border" in options["up"]:
+                # Map border to line.
+                up_line = Shape._get_line_properties(options["up"]["border"])
+
+            if "line" in options["up"]:
+                up_line = Shape._get_line_properties(options["up"]["line"])
+
+            if "fill" in options["up"]:
+                up_fill = Shape._get_fill_properties(options["up"]["fill"])
+
+        # Set properties for 'down' bar.
+        if options.get("down"):
+            if "border" in options["down"]:
+                # Map border to line.
+                down_line = Shape._get_line_properties(options["down"]["border"])
+
+            if "line" in options["down"]:
+                down_line = Shape._get_line_properties(options["down"]["line"])
+
+            if "fill" in options["down"]:
+                down_fill = Shape._get_fill_properties(options["down"]["fill"])
+
+        self.up_down_bars = {
+            "up": {
+                "line": up_line,
+                "fill": up_fill,
+            },
+            "down": {
+                "line": down_line,
+                "fill": down_fill,
+            },
+        }
+
+    def set_drop_lines(self, options=None):
+        """
+        Set properties for the chart drop lines.
+
+        Args:
+            options: A dictionary of options.
+
+        Returns:
+            Nothing.
+
+        """
+        if options is None:
+            options = {}
+
+        line = Shape._get_line_properties(options.get("line"))
+        fill = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        self.drop_lines = {
+            "line": line,
+            "fill": fill,
+            "pattern": pattern,
+            "gradient": gradient,
+        }
+
+    def set_high_low_lines(self, options=None):
+        """
+        Set properties for the chart high-low lines.
+
+        Args:
+            options: A dictionary of options.
+
+        Returns:
+            Nothing.
+
+        """
+        if options is None:
+            options = {}
+
+        line = Shape._get_line_properties(options.get("line"))
+        fill = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        self.hi_low_lines = {
+            "line": line,
+            "fill": fill,
+            "pattern": pattern,
+            "gradient": gradient,
+        }
+
+    def combine(self, chart=None):
+        """
+        Create a combination chart with a secondary chart.
+
+        Args:
+            chart: The secondary chart to combine with the primary chart.
+
+        Returns:
+            Nothing.
+
+        """
+        if chart is None:
+            return
+
+        self.combined = chart
+
+    ###########################################################################
+    #
+    # Private API.
+    #
+    ###########################################################################
+
+    def _assemble_xml_file(self):
+        # Assemble and write the XML file.
+
+        # Write the XML declaration.
+        self._xml_declaration()
+
+        # Write the c:chartSpace element.
+        self._write_chart_space()
+
+        # Write the c:lang element.
+        self._write_lang()
+
+        # Write the c:style element.
+        self._write_style()
+
+        # Write the c:protection element.
+        self._write_protection()
+
+        # Write the c:chart element.
+        self._write_chart()
+
+        # Write the c:spPr element for the chartarea formatting.
+        self._write_sp_pr(self.chartarea)
+
+        # Write the c:printSettings element.
+        if self.embedded:
+            self._write_print_settings()
+
+        # Close the worksheet tag.
+        self._xml_end_tag("c:chartSpace")
+        # Close the file.
+        self._xml_close()
+
+    def _convert_axis_args(self, axis, user_options):
+        # Convert user defined axis values into private hash values.
+        options = axis["defaults"].copy()
+        options.update(user_options)
+
+        name, name_formula = self._process_names(
+            options.get("name"), options.get("name_formula")
+        )
+
+        data_id = self._get_data_id(name_formula, options.get("data"))
+
+        axis = {
+            "defaults": axis["defaults"],
+            "name": name,
+            "formula": name_formula,
+            "data_id": data_id,
+            "reverse": options.get("reverse"),
+            "min": options.get("min"),
+            "max": options.get("max"),
+            "minor_unit": options.get("minor_unit"),
+            "major_unit": options.get("major_unit"),
+            "minor_unit_type": options.get("minor_unit_type"),
+            "major_unit_type": options.get("major_unit_type"),
+            "display_units": options.get("display_units"),
+            "log_base": options.get("log_base"),
+            "crossing": options.get("crossing"),
+            "position_axis": options.get("position_axis"),
+            "position": options.get("position"),
+            "label_position": options.get("label_position"),
+            "label_align": options.get("label_align"),
+            "num_format": options.get("num_format"),
+            "num_format_linked": options.get("num_format_linked"),
+            "interval_unit": options.get("interval_unit"),
+            "interval_tick": options.get("interval_tick"),
+            "text_axis": False,
+        }
+
+        axis["visible"] = options.get("visible", True)
+
+        # Convert the display units.
+        axis["display_units"] = self._get_display_units(axis["display_units"])
+        axis["display_units_visible"] = options.get("display_units_visible", True)
+
+        # Map major_gridlines properties.
+        if options.get("major_gridlines") and options["major_gridlines"]["visible"]:
+            axis["major_gridlines"] = self._get_gridline_properties(
+                options["major_gridlines"]
+            )
+
+        # Map minor_gridlines properties.
+        if options.get("minor_gridlines") and options["minor_gridlines"]["visible"]:
+            axis["minor_gridlines"] = self._get_gridline_properties(
+                options["minor_gridlines"]
+            )
+
+        # Only use the first letter of bottom, top, left or right.
+        if axis.get("position"):
+            axis["position"] = axis["position"].lower()[0]
+
+        # Set the position for a category axis on or between the tick marks.
+        if axis.get("position_axis"):
+            if axis["position_axis"] == "on_tick":
+                axis["position_axis"] = "midCat"
+            elif axis["position_axis"] == "between":
+                # Doesn't need to be modified.
+                pass
+            else:
+                # Otherwise use the default value.
+                axis["position_axis"] = None
+
+        # Set the category axis as a date axis.
+        if options.get("date_axis"):
+            self.date_category = True
+
+        # Set the category axis as a text axis.
+        if options.get("text_axis"):
+            self.date_category = False
+            axis["text_axis"] = True
+
+        # Convert datetime args if required.
+        if axis.get("min") and _supported_datetime(axis["min"]):
+            axis["min"] = _datetime_to_excel_datetime(
+                axis["min"], self.date_1904, self.remove_timezone
+            )
+        if axis.get("max") and _supported_datetime(axis["max"]):
+            axis["max"] = _datetime_to_excel_datetime(
+                axis["max"], self.date_1904, self.remove_timezone
+            )
+        if axis.get("crossing") and _supported_datetime(axis["crossing"]):
+            axis["crossing"] = _datetime_to_excel_datetime(
+                axis["crossing"], self.date_1904, self.remove_timezone
+            )
+
+        # Set the font properties if present.
+        axis["num_font"] = self._convert_font_args(options.get("num_font"))
+        axis["name_font"] = self._convert_font_args(options.get("name_font"))
+
+        # Set the axis name layout.
+        axis["name_layout"] = self._get_layout_properties(
+            options.get("name_layout"), True
+        )
+
+        # Set the line properties for the axis.
+        axis["line"] = Shape._get_line_properties(options.get("line"))
+
+        # Set the fill properties for the axis.
+        axis["fill"] = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        axis["pattern"] = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        axis["gradient"] = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if axis.get("pattern"):
+            axis["fill"] = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if axis.get("gradient"):
+            axis["pattern"] = None
+            axis["fill"] = None
+
+        # Set the tick marker types.
+        axis["minor_tick_mark"] = self._get_tick_type(options.get("minor_tick_mark"))
+        axis["major_tick_mark"] = self._get_tick_type(options.get("major_tick_mark"))
+
+        return axis
+
+    def _convert_font_args(self, options):
+        # Convert user defined font values into private dict values.
+        if not options:
+            return {}
+
+        font = {
+            "name": options.get("name"),
+            "color": options.get("color"),
+            "size": options.get("size"),
+            "bold": options.get("bold"),
+            "italic": options.get("italic"),
+            "underline": options.get("underline"),
+            "pitch_family": options.get("pitch_family"),
+            "charset": options.get("charset"),
+            "baseline": options.get("baseline", 0),
+            "rotation": options.get("rotation"),
+        }
+
+        # Convert font size units.
+        if font["size"]:
+            font["size"] = int(font["size"] * 100)
+
+        # Convert rotation into 60,000ths of a degree.
+        if font["rotation"]:
+            font["rotation"] = 60000 * int(font["rotation"])
+
+        return font
+
+    def _list_to_formula(self, data):
+        # Convert and list of row col values to a range formula.
+
+        # If it isn't an array ref it is probably a formula already.
+        if not isinstance(data, list):
+            # Check for unquoted sheetnames.
+            if data and " " in data and "'" not in data and self.warn_sheetname:
+                warn(
+                    f"Sheetname in '{data}' contains spaces but isn't quoted. "
+                    f"This may cause an error in Excel."
+                )
+            return data
+
+        formula = xl_range_formula(*data)
+
+        return formula
+
+    def _process_names(self, name, name_formula):
+        # Switch name and name_formula parameters if required.
+
+        if name is not None:
+            if isinstance(name, list):
+                # Convert a list of values into a name formula.
+                cell = xl_rowcol_to_cell(name[1], name[2], True, True)
+                name_formula = quote_sheetname(name[0]) + "!" + cell
+                name = ""
+            elif re.match(r"^=?[^!]+!\$?[A-Z]+\$?\d+", name):
+                # Name looks like a formula, use it to set name_formula.
+                name_formula = name
+                name = ""
+
+        return name, name_formula
+
+    def _get_data_type(self, data):
+        # Find the overall type of the data associated with a series.
+
+        # Check for no data in the series.
+        if data is None or len(data) == 0:
+            return "none"
+
+        if isinstance(data[0], list):
+            return "multi_str"
+
+        # Determine if data is numeric or strings.
+        for token in data:
+            if token is None:
+                continue
+
+            # Check for strings that would evaluate to float like
+            # '1.1_1' of ' 1'.
+            if isinstance(token, str) and re.search("[_ ]", token):
+                # Assume entire data series is string data.
+                return "str"
+
+            try:
+                float(token)
+            except ValueError:
+                # Not a number. Assume entire data series is string data.
+                return "str"
+
+        # The series data was all numeric.
+        return "num"
+
+    def _get_data_id(self, formula, data):
+        # Assign an id to a each unique series formula or title/axis formula.
+        # Repeated formulas such as for categories get the same id. If the
+        # series or title has user specified data associated with it then
+        # that is also stored. This data is used to populate cached Excel
+        # data when creating a chart. If there is no user defined data then
+        # it will be populated by the parent Workbook._add_chart_data().
+
+        # Ignore series without a range formula.
+        if not formula:
+            return None
+
+        # Strip the leading '=' from the formula.
+        if formula.startswith("="):
+            formula = formula.lstrip("=")
+
+        # Store the data id in a hash keyed by the formula and store the data
+        # in a separate array with the same id.
+        if formula not in self.formula_ids:
+            # Haven't seen this formula before.
+            formula_id = len(self.formula_data)
+
+            self.formula_data.append(data)
+            self.formula_ids[formula] = formula_id
+        else:
+            # Formula already seen. Return existing id.
+            formula_id = self.formula_ids[formula]
+
+            # Store user defined data if it isn't already there.
+            if self.formula_data[formula_id] is None:
+                self.formula_data[formula_id] = data
+
+        return formula_id
+
+    def _get_marker_properties(self, marker):
+        # Convert user marker properties to the structure required internally.
+
+        if not marker:
+            return None
+
+        # Copy the user defined properties since they will be modified.
+        marker = copy.deepcopy(marker)
+
+        types = {
+            "automatic": "automatic",
+            "none": "none",
+            "square": "square",
+            "diamond": "diamond",
+            "triangle": "triangle",
+            "x": "x",
+            "star": "star",
+            "dot": "dot",
+            "short_dash": "dot",
+            "dash": "dash",
+            "long_dash": "dash",
+            "circle": "circle",
+            "plus": "plus",
+            "picture": "picture",
+        }
+
+        # Check for valid types.
+        marker_type = marker.get("type")
+
+        if marker_type is not None:
+            if marker_type in types:
+                marker["type"] = types[marker_type]
+            else:
+                warn(f"Unknown marker type '{marker_type}")
+                return None
+
+        # Set the line properties for the marker.
+        line = Shape._get_line_properties(marker.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if "border" in marker:
+            line = Shape._get_line_properties(marker["border"])
+
+        # Set the fill properties for the marker.
+        fill = Shape._get_fill_properties(marker.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(marker.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(marker.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        marker["line"] = line
+        marker["fill"] = fill
+        marker["pattern"] = pattern
+        marker["gradient"] = gradient
+
+        return marker
+
+    def _get_trendline_properties(self, trendline):
+        # Convert user trendline properties to structure required internally.
+
+        if not trendline:
+            return None
+
+        # Copy the user defined properties since they will be modified.
+        trendline = copy.deepcopy(trendline)
+
+        types = {
+            "exponential": "exp",
+            "linear": "linear",
+            "log": "log",
+            "moving_average": "movingAvg",
+            "polynomial": "poly",
+            "power": "power",
+        }
+
+        # Check the trendline type.
+        trend_type = trendline.get("type")
+
+        if trend_type in types:
+            trendline["type"] = types[trend_type]
+        else:
+            warn(f"Unknown trendline type '{trend_type}'")
+            return None
+
+        # Set the line properties for the trendline.
+        line = Shape._get_line_properties(trendline.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if "border" in trendline:
+            line = Shape._get_line_properties(trendline["border"])
+
+        # Set the fill properties for the trendline.
+        fill = Shape._get_fill_properties(trendline.get("fill"))
+
+        # Set the pattern fill properties for the trendline.
+        pattern = Shape._get_pattern_properties(trendline.get("pattern"))
+
+        # Set the gradient fill properties for the trendline.
+        gradient = Shape._get_gradient_properties(trendline.get("gradient"))
+
+        # Set the format properties for the trendline label.
+        label = self._get_trendline_label_properties(trendline.get("label"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        trendline["line"] = line
+        trendline["fill"] = fill
+        trendline["pattern"] = pattern
+        trendline["gradient"] = gradient
+        trendline["label"] = label
+
+        return trendline
+
+    def _get_trendline_label_properties(self, label):
+        # Convert user trendline properties to structure required internally.
+
+        if not label:
+            return {}
+
+        # Copy the user defined properties since they will be modified.
+        label = copy.deepcopy(label)
+
+        # Set the font properties if present.
+        font = self._convert_font_args(label.get("font"))
+
+        # Set the line properties for the label.
+        line = Shape._get_line_properties(label.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if "border" in label:
+            line = Shape._get_line_properties(label["border"])
+
+        # Set the fill properties for the label.
+        fill = Shape._get_fill_properties(label.get("fill"))
+
+        # Set the pattern fill properties for the label.
+        pattern = Shape._get_pattern_properties(label.get("pattern"))
+
+        # Set the gradient fill properties for the label.
+        gradient = Shape._get_gradient_properties(label.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        label["font"] = font
+        label["line"] = line
+        label["fill"] = fill
+        label["pattern"] = pattern
+        label["gradient"] = gradient
+
+        return label
+
+    def _get_error_bars_props(self, options):
+        # Convert user error bars properties to structure required internally.
+        if not options:
+            return {}
+
+        # Default values.
+        error_bars = {"type": "fixedVal", "value": 1, "endcap": 1, "direction": "both"}
+
+        types = {
+            "fixed": "fixedVal",
+            "percentage": "percentage",
+            "standard_deviation": "stdDev",
+            "standard_error": "stdErr",
+            "custom": "cust",
+        }
+
+        # Check the error bars type.
+        error_type = options["type"]
+
+        if error_type in types:
+            error_bars["type"] = types[error_type]
+        else:
+            warn(f"Unknown error bars type '{error_type}")
+            return {}
+
+        # Set the value for error types that require it.
+        if "value" in options:
+            error_bars["value"] = options["value"]
+
+        # Set the end-cap style.
+        if "end_style" in options:
+            error_bars["endcap"] = options["end_style"]
+
+        # Set the error bar direction.
+        if "direction" in options:
+            if options["direction"] == "minus":
+                error_bars["direction"] = "minus"
+            elif options["direction"] == "plus":
+                error_bars["direction"] = "plus"
+            else:
+                # Default to 'both'.
+                pass
+
+        # Set any custom values.
+        error_bars["plus_values"] = options.get("plus_values")
+        error_bars["minus_values"] = options.get("minus_values")
+        error_bars["plus_data"] = options.get("plus_data")
+        error_bars["minus_data"] = options.get("minus_data")
+
+        # Set the line properties for the error bars.
+        error_bars["line"] = Shape._get_line_properties(options.get("line"))
+
+        return error_bars
+
+    def _get_gridline_properties(self, options):
+        # Convert user gridline properties to structure required internally.
+
+        # Set the visible property for the gridline.
+        gridline = {"visible": options.get("visible")}
+
+        # Set the line properties for the gridline.
+        gridline["line"] = Shape._get_line_properties(options.get("line"))
+
+        return gridline
+
+    def _get_labels_properties(self, labels):
+        # Convert user labels properties to the structure required internally.
+
+        if not labels:
+            return None
+
+        # Copy the user defined properties since they will be modified.
+        labels = copy.deepcopy(labels)
+
+        # Map user defined label positions to Excel positions.
+        position = labels.get("position")
+
+        if position:
+            if position in self.label_positions:
+                if position == self.label_position_default:
+                    labels["position"] = None
+                else:
+                    labels["position"] = self.label_positions[position]
+            else:
+                warn(f"Unsupported label position '{position}' for this chart type")
+                return None
+
+        # Map the user defined label separator to the Excel separator.
+        separator = labels.get("separator")
+        separators = {
+            ",": ", ",
+            ";": "; ",
+            ".": ". ",
+            "\n": "\n",
+            " ": " ",
+        }
+
+        if separator:
+            if separator in separators:
+                labels["separator"] = separators[separator]
+            else:
+                warn("Unsupported label separator")
+                return None
+
+        # Set the font properties if present.
+        labels["font"] = self._convert_font_args(labels.get("font"))
+
+        # Set the line properties for the labels.
+        line = Shape._get_line_properties(labels.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if "border" in labels:
+            line = Shape._get_line_properties(labels["border"])
+
+        # Set the fill properties for the labels.
+        fill = Shape._get_fill_properties(labels.get("fill"))
+
+        # Set the pattern fill properties for the labels.
+        pattern = Shape._get_pattern_properties(labels.get("pattern"))
+
+        # Set the gradient fill properties for the labels.
+        gradient = Shape._get_gradient_properties(labels.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        labels["line"] = line
+        labels["fill"] = fill
+        labels["pattern"] = pattern
+        labels["gradient"] = gradient
+
+        if labels.get("custom"):
+            for label in labels["custom"]:
+                if label is None:
+                    continue
+
+                value = label.get("value")
+                if value and re.match(r"^=?[^!]+!\$?[A-Z]+\$?\d+", str(value)):
+                    label["formula"] = value
+
+                formula = label.get("formula")
+                if formula and formula.startswith("="):
+                    label["formula"] = formula.lstrip("=")
+
+                data_id = self._get_data_id(formula, label.get("data"))
+                label["data_id"] = data_id
+
+                label["font"] = self._convert_font_args(label.get("font"))
+
+                # Set the line properties for the label.
+                line = Shape._get_line_properties(label.get("line"))
+
+                # Allow 'border' as a synonym for 'line'.
+                if "border" in label:
+                    line = Shape._get_line_properties(label["border"])
+
+                # Set the fill properties for the label.
+                fill = Shape._get_fill_properties(label.get("fill"))
+
+                # Set the pattern fill properties for the label.
+                pattern = Shape._get_pattern_properties(label.get("pattern"))
+
+                # Set the gradient fill properties for the label.
+                gradient = Shape._get_gradient_properties(label.get("gradient"))
+
+                # Pattern fill overrides solid fill.
+                if pattern:
+                    self.fill = None
+
+                # Gradient fill overrides the solid and pattern fill.
+                if gradient:
+                    pattern = None
+                    fill = None
+
+                label["line"] = line
+                label["fill"] = fill
+                label["pattern"] = pattern
+                label["gradient"] = gradient
+
+        return labels
+
+    def _get_area_properties(self, options):
+        # Convert user area properties to the structure required internally.
+        area = {}
+
+        # Set the line properties for the chartarea.
+        line = Shape._get_line_properties(options.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if options.get("border"):
+            line = Shape._get_line_properties(options["border"])
+
+        # Set the fill properties for the chartarea.
+        fill = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        # Set the plotarea layout.
+        layout = self._get_layout_properties(options.get("layout"), False)
+
+        area["line"] = line
+        area["fill"] = fill
+        area["pattern"] = pattern
+        area["layout"] = layout
+        area["gradient"] = gradient
+
+        return area
+
+    def _get_legend_properties(self, options=None):
+        # Convert user legend properties to the structure required internally.
+        legend = {}
+
+        if options is None:
+            options = {}
+
+        legend["position"] = options.get("position", "right")
+        legend["delete_series"] = options.get("delete_series")
+        legend["font"] = self._convert_font_args(options.get("font"))
+        legend["layout"] = self._get_layout_properties(options.get("layout"), False)
+
+        # Turn off the legend.
+        if options.get("none"):
+            legend["position"] = "none"
+
+        # Set the line properties for the legend.
+        line = Shape._get_line_properties(options.get("line"))
+
+        # Allow 'border' as a synonym for 'line'.
+        if options.get("border"):
+            line = Shape._get_line_properties(options["border"])
+
+        # Set the fill properties for the legend.
+        fill = Shape._get_fill_properties(options.get("fill"))
+
+        # Set the pattern fill properties for the series.
+        pattern = Shape._get_pattern_properties(options.get("pattern"))
+
+        # Set the gradient fill properties for the series.
+        gradient = Shape._get_gradient_properties(options.get("gradient"))
+
+        # Pattern fill overrides solid fill.
+        if pattern:
+            self.fill = None
+
+        # Gradient fill overrides the solid and pattern fill.
+        if gradient:
+            pattern = None
+            fill = None
+
+        # Set the legend layout.
+        layout = self._get_layout_properties(options.get("layout"), False)
+
+        legend["line"] = line
+        legend["fill"] = fill
+        legend["pattern"] = pattern
+        legend["layout"] = layout
+        legend["gradient"] = gradient
+
+        return legend
+
+    def _get_layout_properties(self, args, is_text):
+        # Convert user defined layout properties to format used internally.
+        layout = {}
+
+        if not args:
+            return {}
+
+        if is_text:
+            properties = ("x", "y")
+        else:
+            properties = ("x", "y", "width", "height")
+
+        # Check for valid properties.
+        for key in args.keys():
+            if key not in properties:
+                warn(f"Property '{key}' not supported in layout options")
+                return {}
+
+        # Set the layout properties.
+        for prop in properties:
+            if prop not in args.keys():
+                warn(f"Property '{prop}' must be specified in layout options")
+                return {}
+
+            value = args[prop]
+
+            try:
+                float(value)
+            except ValueError:
+                warn(f"Property '{prop}' value '{value}' must be numeric in layout")
+                return {}
+
+            if value < 0 or value > 1:
+                warn(
+                    f"Property '{prop}' value '{value}' must be in range "
+                    f"0 < x <= 1 in layout options"
+                )
+                return {}
+
+            # Convert to the format used by Excel for easier testing
+            layout[prop] = f"{value:.17g}"
+
+        return layout
+
+    def _get_points_properties(self, user_points):
+        # Convert user points properties to structure required internally.
+        points = []
+
+        if not user_points:
+            return []
+
+        for user_point in user_points:
+            point = {}
+
+            if user_point is not None:
+                # Set the line properties for the point.
+                line = Shape._get_line_properties(user_point.get("line"))
+
+                # Allow 'border' as a synonym for 'line'.
+                if "border" in user_point:
+                    line = Shape._get_line_properties(user_point["border"])
+
+                # Set the fill properties for the chartarea.
+                fill = Shape._get_fill_properties(user_point.get("fill"))
+
+                # Set the pattern fill properties for the series.
+                pattern = Shape._get_pattern_properties(user_point.get("pattern"))
+
+                # Set the gradient fill properties for the series.
+                gradient = Shape._get_gradient_properties(user_point.get("gradient"))
+
+                # Pattern fill overrides solid fill.
+                if pattern:
+                    self.fill = None
+
+                # Gradient fill overrides the solid and pattern fill.
+                if gradient:
+                    pattern = None
+                    fill = None
+
+                point["line"] = line
+                point["fill"] = fill
+                point["pattern"] = pattern
+                point["gradient"] = gradient
+
+            points.append(point)
+
+        return points
+
+    def _has_fill_formatting(self, element):
+        # Check if a chart element has line, fill or gradient formatting.
+        has_fill = False
+        has_line = False
+        has_pattern = element.get("pattern")
+        has_gradient = element.get("gradient")
+
+        if element.get("fill") and element["fill"]["defined"]:
+            has_fill = True
+
+        if element.get("line") and element["line"]["defined"]:
+            has_line = True
+
+        return has_fill or has_line or has_pattern or has_gradient
+
+    def _get_display_units(self, display_units):
+        # Convert user defined display units to internal units.
+        if not display_units:
+            return None
+
+        types = {
+            "hundreds": "hundreds",
+            "thousands": "thousands",
+            "ten_thousands": "tenThousands",
+            "hundred_thousands": "hundredThousands",
+            "millions": "millions",
+            "ten_millions": "tenMillions",
+            "hundred_millions": "hundredMillions",
+            "billions": "billions",
+            "trillions": "trillions",
+        }
+
+        if display_units in types:
+            display_units = types[display_units]
+        else:
+            warn(f"Unknown display_units type '{display_units}'")
+            return None
+
+        return display_units
+
+    def _get_tick_type(self, tick_type):
+        # Convert user defined display units to internal units.
+        if not tick_type:
+            return None
+
+        types = {
+            "outside": "out",
+            "inside": "in",
+            "none": "none",
+            "cross": "cross",
+        }
+
+        if tick_type in types:
+            tick_type = types[tick_type]
+        else:
+            warn(f"Unknown tick_type '{tick_type}'")
+            return None
+
+        return tick_type
+
+    def _get_primary_axes_series(self):
+        # Returns series which use the primary axes.
+        primary_axes_series = []
+
+        for series in self.series:
+            if not series["y2_axis"]:
+                primary_axes_series.append(series)
+
+        return primary_axes_series
+
+    def _get_secondary_axes_series(self):
+        # Returns series which use the secondary axes.
+        secondary_axes_series = []
+
+        for series in self.series:
+            if series["y2_axis"]:
+                secondary_axes_series.append(series)
+
+        return secondary_axes_series
+
+    def _add_axis_ids(self, args):
+        # Add unique ids for primary or secondary axes
+        chart_id = 5001 + int(self.id)
+        axis_count = 1 + len(self.axis2_ids) + len(self.axis_ids)
+
+        id1 = f"{chart_id:04d}{axis_count:04d}"
+        id2 = f"{chart_id:04d}{axis_count + 1:04d}"
+
+        if args["primary_axes"]:
+            self.axis_ids.append(id1)
+            self.axis_ids.append(id2)
+
+        if not args["primary_axes"]:
+            self.axis2_ids.append(id1)
+            self.axis2_ids.append(id2)
+
+    def _set_default_properties(self):
+        # Setup the default properties for a chart.
+
+        self.x_axis["defaults"] = {
+            "num_format": "General",
+            "major_gridlines": {"visible": 0},
+        }
+
+        self.y_axis["defaults"] = {
+            "num_format": "General",
+            "major_gridlines": {"visible": 1},
+        }
+
+        self.x2_axis["defaults"] = {
+            "num_format": "General",
+            "label_position": "none",
+            "crossing": "max",
+            "visible": 0,
+        }
+
+        self.y2_axis["defaults"] = {
+            "num_format": "General",
+            "major_gridlines": {"visible": 0},
+            "position": "right",
+            "visible": 1,
+        }
+
+        self.set_x_axis({})
+        self.set_y_axis({})
+
+        self.set_x2_axis({})
+        self.set_y2_axis({})
+
+    ###########################################################################
+    #
+    # XML methods.
+    #
+    ###########################################################################
+
+    def _write_chart_space(self):
+        # Write the <c:chartSpace> element.
+        schema = "http://schemas.openxmlformats.org/"
+        xmlns_c = schema + "drawingml/2006/chart"
+        xmlns_a = schema + "drawingml/2006/main"
+        xmlns_r = schema + "officeDocument/2006/relationships"
+
+        attributes = [
+            ("xmlns:c", xmlns_c),
+            ("xmlns:a", xmlns_a),
+            ("xmlns:r", xmlns_r),
+        ]
+
+        self._xml_start_tag("c:chartSpace", attributes)
+
+    def _write_lang(self):
+        # Write the <c:lang> element.
+        val = "en-US"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:lang", attributes)
+
+    def _write_style(self):
+        # Write the <c:style> element.
+        style_id = self.style_id
+
+        # Don't write an element for the default style, 2.
+        if style_id == 2:
+            return
+
+        attributes = [("val", style_id)]
+
+        self._xml_empty_tag("c:style", attributes)
+
+    def _write_chart(self):
+        # Write the <c:chart> element.
+        self._xml_start_tag("c:chart")
+
+        if self.title_none:
+            # Turn off the title.
+            self._write_c_auto_title_deleted()
+        else:
+            # Write the chart title elements.
+            if self.title_formula is not None:
+                self._write_title_formula(
+                    self.title_formula,
+                    self.title_data_id,
+                    None,
+                    self.title_font,
+                    self.title_layout,
+                    self.title_overlay,
+                )
+            elif self.title_name is not None:
+                self._write_title_rich(
+                    self.title_name,
+                    None,
+                    self.title_font,
+                    self.title_layout,
+                    self.title_overlay,
+                )
+
+        # Write the c:plotArea element.
+        self._write_plot_area()
+
+        # Write the c:legend element.
+        self._write_legend()
+
+        # Write the c:plotVisOnly element.
+        self._write_plot_vis_only()
+
+        # Write the c:dispBlanksAs element.
+        self._write_disp_blanks_as()
+
+        # Write the c:extLst element.
+        if self.show_na_as_empty:
+            self._write_c_ext_lst_display_na()
+
+        self._xml_end_tag("c:chart")
+
+    def _write_disp_blanks_as(self):
+        # Write the <c:dispBlanksAs> element.
+        val = self.show_blanks
+
+        # Ignore the default value.
+        if val == "gap":
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:dispBlanksAs", attributes)
+
+    def _write_plot_area(self):
+        # Write the <c:plotArea> element.
+        self._xml_start_tag("c:plotArea")
+
+        # Write the c:layout element.
+        self._write_layout(self.plotarea.get("layout"), "plot")
+
+        # Write  subclass chart type elements for primary and secondary axes.
+        self._write_chart_type({"primary_axes": True})
+        self._write_chart_type({"primary_axes": False})
+
+        # Configure a combined chart if present.
+        second_chart = self.combined
+        if second_chart:
+            # Secondary axis has unique id otherwise use same as primary.
+            if second_chart.is_secondary:
+                second_chart.id = 1000 + self.id
+            else:
+                second_chart.id = self.id
+
+            # Share the same filehandle for writing.
+            second_chart.fh = self.fh
+
+            # Share series index with primary chart.
+            second_chart.series_index = self.series_index
+
+            # Write the subclass chart type elements for combined chart.
+            second_chart._write_chart_type({"primary_axes": True})
+            second_chart._write_chart_type({"primary_axes": False})
+
+        # Write the category and value elements for the primary axes.
+        args = {"x_axis": self.x_axis, "y_axis": self.y_axis, "axis_ids": self.axis_ids}
+
+        if self.date_category:
+            self._write_date_axis(args)
+        else:
+            self._write_cat_axis(args)
+
+        self._write_val_axis(args)
+
+        # Write the category and value elements for the secondary axes.
+        args = {
+            "x_axis": self.x2_axis,
+            "y_axis": self.y2_axis,
+            "axis_ids": self.axis2_ids,
+        }
+
+        self._write_val_axis(args)
+
+        # Write the secondary axis for the secondary chart.
+        if second_chart and second_chart.is_secondary:
+            args = {
+                "x_axis": second_chart.x2_axis,
+                "y_axis": second_chart.y2_axis,
+                "axis_ids": second_chart.axis2_ids,
+            }
+
+            second_chart._write_val_axis(args)
+
+        if self.date_category:
+            self._write_date_axis(args)
+        else:
+            self._write_cat_axis(args)
+
+        # Write the c:dTable element.
+        self._write_d_table()
+
+        # Write the c:spPr element for the plotarea formatting.
+        self._write_sp_pr(self.plotarea)
+
+        self._xml_end_tag("c:plotArea")
+
+    def _write_layout(self, layout, layout_type):
+        # Write the <c:layout> element.
+
+        if not layout:
+            # Automatic layout.
+            self._xml_empty_tag("c:layout")
+        else:
+            # User defined manual layout.
+            self._xml_start_tag("c:layout")
+            self._write_manual_layout(layout, layout_type)
+            self._xml_end_tag("c:layout")
+
+    def _write_manual_layout(self, layout, layout_type):
+        # Write the <c:manualLayout> element.
+        self._xml_start_tag("c:manualLayout")
+
+        # Plotarea has a layoutTarget element.
+        if layout_type == "plot":
+            self._xml_empty_tag("c:layoutTarget", [("val", "inner")])
+
+        # Set the x, y positions.
+        self._xml_empty_tag("c:xMode", [("val", "edge")])
+        self._xml_empty_tag("c:yMode", [("val", "edge")])
+        self._xml_empty_tag("c:x", [("val", layout["x"])])
+        self._xml_empty_tag("c:y", [("val", layout["y"])])
+
+        # For plotarea and legend set the width and height.
+        if layout_type != "text":
+            self._xml_empty_tag("c:w", [("val", layout["width"])])
+            self._xml_empty_tag("c:h", [("val", layout["height"])])
+
+        self._xml_end_tag("c:manualLayout")
+
+    def _write_chart_type(self, args):
+        # pylint: disable=unused-argument
+        # Write the chart type element. This method should be overridden
+        # by the subclasses.
+        return
+
+    def _write_grouping(self, val):
+        # Write the <c:grouping> element.
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:grouping", attributes)
+
+    def _write_series(self, series):
+        # Write the series elements.
+        self._write_ser(series)
+
+    def _write_ser(self, series):
+        # Write the <c:ser> element.
+        index = self.series_index
+        self.series_index += 1
+
+        self._xml_start_tag("c:ser")
+
+        # Write the c:idx element.
+        self._write_idx(index)
+
+        # Write the c:order element.
+        self._write_order(index)
+
+        # Write the series name.
+        self._write_series_name(series)
+
+        # Write the c:spPr element.
+        self._write_sp_pr(series)
+
+        # Write the c:marker element.
+        self._write_marker(series["marker"])
+
+        # Write the c:invertIfNegative element.
+        self._write_c_invert_if_negative(series["invert_if_neg"])
+
+        # Write the c:dPt element.
+        self._write_d_pt(series["points"])
+
+        # Write the c:dLbls element.
+        self._write_d_lbls(series["labels"])
+
+        # Write the c:trendline element.
+        self._write_trendline(series["trendline"])
+
+        # Write the c:errBars element.
+        self._write_error_bars(series["error_bars"])
+
+        # Write the c:cat element.
+        self._write_cat(series)
+
+        # Write the c:val element.
+        self._write_val(series)
+
+        # Write the c:smooth element.
+        if self.smooth_allowed:
+            self._write_c_smooth(series["smooth"])
+
+        # Write the c:extLst element.
+        if series.get("inverted_color"):
+            self._write_c_ext_lst_inverted_color(series["inverted_color"])
+
+        self._xml_end_tag("c:ser")
+
+    def _write_c_ext_lst_inverted_color(self, color):
+        # Write the <c:extLst> element for the inverted fill color.
+
+        uri = "{6F2FDCE9-48DA-4B69-8628-5D25D57E5C99}"
+        xmlns_c_14 = "http://schemas.microsoft.com/office/drawing/2007/8/2/chart"
+
+        attributes1 = [
+            ("uri", uri),
+            ("xmlns:c14", xmlns_c_14),
+        ]
+
+        attributes2 = [("xmlns:c14", xmlns_c_14)]
+
+        self._xml_start_tag("c:extLst")
+        self._xml_start_tag("c:ext", attributes1)
+        self._xml_start_tag("c14:invertSolidFillFmt")
+        self._xml_start_tag("c14:spPr", attributes2)
+
+        self._write_a_solid_fill({"color": color})
+
+        self._xml_end_tag("c14:spPr")
+        self._xml_end_tag("c14:invertSolidFillFmt")
+        self._xml_end_tag("c:ext")
+        self._xml_end_tag("c:extLst")
+
+    def _write_c_ext_lst_display_na(self):
+        # Write the <c:extLst> element for the display NA as empty cell option.
+
+        uri = "{56B9EC1D-385E-4148-901F-78D8002777C0}"
+        xmlns_c_16 = "http://schemas.microsoft.com/office/drawing/2017/03/chart"
+
+        attributes1 = [
+            ("uri", uri),
+            ("xmlns:c16r3", xmlns_c_16),
+        ]
+
+        attributes2 = [("val", 1)]
+
+        self._xml_start_tag("c:extLst")
+        self._xml_start_tag("c:ext", attributes1)
+        self._xml_start_tag("c16r3:dataDisplayOptions16")
+        self._xml_empty_tag("c16r3:dispNaAsBlank", attributes2)
+        self._xml_end_tag("c16r3:dataDisplayOptions16")
+        self._xml_end_tag("c:ext")
+        self._xml_end_tag("c:extLst")
+
+    def _write_idx(self, val):
+        # Write the <c:idx> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:idx", attributes)
+
+    def _write_order(self, val):
+        # Write the <c:order> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:order", attributes)
+
+    def _write_series_name(self, series):
+        # Write the series name.
+
+        if series["name_formula"] is not None:
+            self._write_tx_formula(series["name_formula"], series["name_id"])
+        elif series["name"] is not None:
+            self._write_tx_value(series["name"])
+
+    def _write_c_smooth(self, smooth):
+        # Write the <c:smooth> element.
+
+        if smooth:
+            self._xml_empty_tag("c:smooth", [("val", "1")])
+
+    def _write_cat(self, series):
+        # Write the <c:cat> element.
+        formula = series["categories"]
+        data_id = series["cat_data_id"]
+        data = None
+
+        if data_id is not None:
+            data = self.formula_data[data_id]
+
+        # Ignore <c:cat> elements for charts without category values.
+        if not formula:
+            return
+
+        self._xml_start_tag("c:cat")
+
+        # Check the type of cached data.
+        cat_type = self._get_data_type(data)
+
+        if cat_type == "str":
+            self.cat_has_num_fmt = 0
+            # Write the c:numRef element.
+            self._write_str_ref(formula, data, cat_type)
+
+        elif cat_type == "multi_str":
+            self.cat_has_num_fmt = 0
+            # Write the c:numRef element.
+            self._write_multi_lvl_str_ref(formula, data)
+
+        else:
+            self.cat_has_num_fmt = 1
+            # Write the c:numRef element.
+            self._write_num_ref(formula, data, cat_type)
+
+        self._xml_end_tag("c:cat")
+
+    def _write_val(self, series):
+        # Write the <c:val> element.
+        formula = series["values"]
+        data_id = series["val_data_id"]
+        data = self.formula_data[data_id]
+
+        self._xml_start_tag("c:val")
+
+        # Unlike Cat axes data should only be numeric.
+        # Write the c:numRef element.
+        self._write_num_ref(formula, data, "num")
+
+        self._xml_end_tag("c:val")
+
+    def _write_num_ref(self, formula, data, ref_type):
+        # Write the <c:numRef> element.
+        self._xml_start_tag("c:numRef")
+
+        # Write the c:f element.
+        self._write_series_formula(formula)
+
+        if ref_type == "num":
+            # Write the c:numCache element.
+            self._write_num_cache(data)
+        elif ref_type == "str":
+            # Write the c:strCache element.
+            self._write_str_cache(data)
+
+        self._xml_end_tag("c:numRef")
+
+    def _write_str_ref(self, formula, data, ref_type):
+        # Write the <c:strRef> element.
+
+        self._xml_start_tag("c:strRef")
+
+        # Write the c:f element.
+        self._write_series_formula(formula)
+
+        if ref_type == "num":
+            # Write the c:numCache element.
+            self._write_num_cache(data)
+        elif ref_type == "str":
+            # Write the c:strCache element.
+            self._write_str_cache(data)
+
+        self._xml_end_tag("c:strRef")
+
+    def _write_multi_lvl_str_ref(self, formula, data):
+        # Write the <c:multiLvlStrRef> element.
+
+        if not data:
+            return
+
+        self._xml_start_tag("c:multiLvlStrRef")
+
+        # Write the c:f element.
+        self._write_series_formula(formula)
+
+        self._xml_start_tag("c:multiLvlStrCache")
+
+        # Write the c:ptCount element.
+        count = len(data[-1])
+        self._write_pt_count(count)
+
+        for cat_data in reversed(data):
+            self._xml_start_tag("c:lvl")
+
+            for i, point in enumerate(cat_data):
+                # Write the c:pt element.
+                self._write_pt(i, point)
+
+            self._xml_end_tag("c:lvl")
+
+        self._xml_end_tag("c:multiLvlStrCache")
+        self._xml_end_tag("c:multiLvlStrRef")
+
+    def _write_series_formula(self, formula):
+        # Write the <c:f> element.
+
+        # Strip the leading '=' from the formula.
+        if formula.startswith("="):
+            formula = formula.lstrip("=")
+
+        self._xml_data_element("c:f", formula)
+
+    def _write_axis_ids(self, args):
+        # Write the <c:axId> elements for the primary or secondary axes.
+
+        # Generate the axis ids.
+        self._add_axis_ids(args)
+
+        if args["primary_axes"]:
+            # Write the axis ids for the primary axes.
+            self._write_axis_id(self.axis_ids[0])
+            self._write_axis_id(self.axis_ids[1])
+        else:
+            # Write the axis ids for the secondary axes.
+            self._write_axis_id(self.axis2_ids[0])
+            self._write_axis_id(self.axis2_ids[1])
+
+    def _write_axis_id(self, val):
+        # Write the <c:axId> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:axId", attributes)
+
+    def _write_cat_axis(self, args):
+        # Write the <c:catAx> element. Usually the X axis.
+        x_axis = args["x_axis"]
+        y_axis = args["y_axis"]
+        axis_ids = args["axis_ids"]
+
+        # If there are no axis_ids then we don't need to write this element.
+        if axis_ids is None or not axis_ids:
+            return
+
+        position = self.cat_axis_position
+        is_y_axis = self.horiz_cat_axis
+
+        # Overwrite the default axis position with a user supplied value.
+        if x_axis.get("position"):
+            position = x_axis["position"]
+
+        self._xml_start_tag("c:catAx")
+
+        self._write_axis_id(axis_ids[0])
+
+        # Write the c:scaling element.
+        self._write_scaling(x_axis.get("reverse"), None, None, None)
+
+        if not x_axis.get("visible"):
+            self._write_delete(1)
+
+        # Write the c:axPos element.
+        self._write_axis_pos(position, y_axis.get("reverse"))
+
+        # Write the c:majorGridlines element.
+        self._write_major_gridlines(x_axis.get("major_gridlines"))
+
+        # Write the c:minorGridlines element.
+        self._write_minor_gridlines(x_axis.get("minor_gridlines"))
+
+        # Write the axis title elements.
+        if x_axis["formula"] is not None:
+            self._write_title_formula(
+                x_axis["formula"],
+                x_axis["data_id"],
+                is_y_axis,
+                x_axis["name_font"],
+                x_axis["name_layout"],
+            )
+        elif x_axis["name"] is not None:
+            self._write_title_rich(
+                x_axis["name"], is_y_axis, x_axis["name_font"], x_axis["name_layout"]
+            )
+
+        # Write the c:numFmt element.
+        self._write_cat_number_format(x_axis)
+
+        # Write the c:majorTickMark element.
+        self._write_major_tick_mark(x_axis.get("major_tick_mark"))
+
+        # Write the c:minorTickMark element.
+        self._write_minor_tick_mark(x_axis.get("minor_tick_mark"))
+
+        # Write the c:tickLblPos element.
+        self._write_tick_label_pos(x_axis.get("label_position"))
+
+        # Write the c:spPr element for the axis line.
+        self._write_sp_pr(x_axis)
+
+        # Write the axis font elements.
+        self._write_axis_font(x_axis.get("num_font"))
+
+        # Write the c:crossAx element.
+        self._write_cross_axis(axis_ids[1])
+
+        if self.show_crosses or x_axis.get("visible"):
+            # Note, the category crossing comes from the value axis.
+            if (
+                y_axis.get("crossing") is None
+                or y_axis.get("crossing") == "max"
+                or y_axis["crossing"] == "min"
+            ):
+                # Write the c:crosses element.
+                self._write_crosses(y_axis.get("crossing"))
+            else:
+                # Write the c:crossesAt element.
+                self._write_c_crosses_at(y_axis.get("crossing"))
+
+        # Write the c:auto element.
+        if not x_axis.get("text_axis"):
+            self._write_auto(1)
+
+        # Write the c:labelAlign element.
+        self._write_label_align(x_axis.get("label_align"))
+
+        # Write the c:labelOffset element.
+        self._write_label_offset(100)
+
+        # Write the c:tickLblSkip element.
+        self._write_c_tick_lbl_skip(x_axis.get("interval_unit"))
+
+        # Write the c:tickMarkSkip element.
+        self._write_c_tick_mark_skip(x_axis.get("interval_tick"))
+
+        self._xml_end_tag("c:catAx")
+
+    def _write_val_axis(self, args):
+        # Write the <c:valAx> element. Usually the Y axis.
+        x_axis = args["x_axis"]
+        y_axis = args["y_axis"]
+        axis_ids = args["axis_ids"]
+        position = args.get("position", self.val_axis_position)
+        is_y_axis = self.horiz_val_axis
+
+        # If there are no axis_ids then we don't need to write this element.
+        if axis_ids is None or not axis_ids:
+            return
+
+        # Overwrite the default axis position with a user supplied value.
+        position = y_axis.get("position") or position
+
+        self._xml_start_tag("c:valAx")
+
+        self._write_axis_id(axis_ids[1])
+
+        # Write the c:scaling element.
+        self._write_scaling(
+            y_axis.get("reverse"),
+            y_axis.get("min"),
+            y_axis.get("max"),
+            y_axis.get("log_base"),
+        )
+
+        if not y_axis.get("visible"):
+            self._write_delete(1)
+
+        # Write the c:axPos element.
+        self._write_axis_pos(position, x_axis.get("reverse"))
+
+        # Write the c:majorGridlines element.
+        self._write_major_gridlines(y_axis.get("major_gridlines"))
+
+        # Write the c:minorGridlines element.
+        self._write_minor_gridlines(y_axis.get("minor_gridlines"))
+
+        # Write the axis title elements.
+        if y_axis["formula"] is not None:
+            self._write_title_formula(
+                y_axis["formula"],
+                y_axis["data_id"],
+                is_y_axis,
+                y_axis["name_font"],
+                y_axis["name_layout"],
+            )
+        elif y_axis["name"] is not None:
+            self._write_title_rich(
+                y_axis["name"],
+                is_y_axis,
+                y_axis.get("name_font"),
+                y_axis.get("name_layout"),
+            )
+
+        # Write the c:numberFormat element.
+        self._write_number_format(y_axis)
+
+        # Write the c:majorTickMark element.
+        self._write_major_tick_mark(y_axis.get("major_tick_mark"))
+
+        # Write the c:minorTickMark element.
+        self._write_minor_tick_mark(y_axis.get("minor_tick_mark"))
+
+        # Write the c:tickLblPos element.
+        self._write_tick_label_pos(y_axis.get("label_position"))
+
+        # Write the c:spPr element for the axis line.
+        self._write_sp_pr(y_axis)
+
+        # Write the axis font elements.
+        self._write_axis_font(y_axis.get("num_font"))
+
+        # Write the c:crossAx element.
+        self._write_cross_axis(axis_ids[0])
+
+        # Note, the category crossing comes from the value axis.
+        if (
+            x_axis.get("crossing") is None
+            or x_axis["crossing"] == "max"
+            or x_axis["crossing"] == "min"
+        ):
+            # Write the c:crosses element.
+            self._write_crosses(x_axis.get("crossing"))
+        else:
+            # Write the c:crossesAt element.
+            self._write_c_crosses_at(x_axis.get("crossing"))
+
+        # Write the c:crossBetween element.
+        self._write_cross_between(x_axis.get("position_axis"))
+
+        # Write the c:majorUnit element.
+        self._write_c_major_unit(y_axis.get("major_unit"))
+
+        # Write the c:minorUnit element.
+        self._write_c_minor_unit(y_axis.get("minor_unit"))
+
+        # Write the c:dispUnits element.
+        self._write_disp_units(
+            y_axis.get("display_units"), y_axis.get("display_units_visible")
+        )
+
+        self._xml_end_tag("c:valAx")
+
+    def _write_cat_val_axis(self, args):
+        # Write the <c:valAx> element. This is for the second valAx
+        # in scatter plots. Usually the X axis.
+        x_axis = args["x_axis"]
+        y_axis = args["y_axis"]
+        axis_ids = args["axis_ids"]
+        position = args["position"] or self.val_axis_position
+        is_y_axis = self.horiz_val_axis
+
+        # If there are no axis_ids then we don't need to write this element.
+        if axis_ids is None or not axis_ids:
+            return
+
+        # Overwrite the default axis position with a user supplied value.
+        position = x_axis.get("position") or position
+
+        self._xml_start_tag("c:valAx")
+
+        self._write_axis_id(axis_ids[0])
+
+        # Write the c:scaling element.
+        self._write_scaling(
+            x_axis.get("reverse"),
+            x_axis.get("min"),
+            x_axis.get("max"),
+            x_axis.get("log_base"),
+        )
+
+        if not x_axis.get("visible"):
+            self._write_delete(1)
+
+        # Write the c:axPos element.
+        self._write_axis_pos(position, y_axis.get("reverse"))
+
+        # Write the c:majorGridlines element.
+        self._write_major_gridlines(x_axis.get("major_gridlines"))
+
+        # Write the c:minorGridlines element.
+        self._write_minor_gridlines(x_axis.get("minor_gridlines"))
+
+        # Write the axis title elements.
+        if x_axis["formula"] is not None:
+            self._write_title_formula(
+                x_axis["formula"],
+                x_axis["data_id"],
+                is_y_axis,
+                x_axis["name_font"],
+                x_axis["name_layout"],
+            )
+        elif x_axis["name"] is not None:
+            self._write_title_rich(
+                x_axis["name"], is_y_axis, x_axis["name_font"], x_axis["name_layout"]
+            )
+
+        # Write the c:numberFormat element.
+        self._write_number_format(x_axis)
+
+        # Write the c:majorTickMark element.
+        self._write_major_tick_mark(x_axis.get("major_tick_mark"))
+
+        # Write the c:minorTickMark element.
+        self._write_minor_tick_mark(x_axis.get("minor_tick_mark"))
+
+        # Write the c:tickLblPos element.
+        self._write_tick_label_pos(x_axis.get("label_position"))
+
+        # Write the c:spPr element for the axis line.
+        self._write_sp_pr(x_axis)
+
+        # Write the axis font elements.
+        self._write_axis_font(x_axis.get("num_font"))
+
+        # Write the c:crossAx element.
+        self._write_cross_axis(axis_ids[1])
+
+        # Note, the category crossing comes from the value axis.
+        if (
+            y_axis.get("crossing") is None
+            or y_axis["crossing"] == "max"
+            or y_axis["crossing"] == "min"
+        ):
+            # Write the c:crosses element.
+            self._write_crosses(y_axis.get("crossing"))
+        else:
+            # Write the c:crossesAt element.
+            self._write_c_crosses_at(y_axis.get("crossing"))
+
+        # Write the c:crossBetween element.
+        self._write_cross_between(y_axis.get("position_axis"))
+
+        # Write the c:majorUnit element.
+        self._write_c_major_unit(x_axis.get("major_unit"))
+
+        # Write the c:minorUnit element.
+        self._write_c_minor_unit(x_axis.get("minor_unit"))
+
+        # Write the c:dispUnits element.
+        self._write_disp_units(
+            x_axis.get("display_units"), x_axis.get("display_units_visible")
+        )
+
+        self._xml_end_tag("c:valAx")
+
+    def _write_date_axis(self, args):
+        # Write the <c:dateAx> element. Usually the X axis.
+        x_axis = args["x_axis"]
+        y_axis = args["y_axis"]
+        axis_ids = args["axis_ids"]
+
+        # If there are no axis_ids then we don't need to write this element.
+        if axis_ids is None or not axis_ids:
+            return
+
+        position = self.cat_axis_position
+
+        # Overwrite the default axis position with a user supplied value.
+        position = x_axis.get("position") or position
+
+        self._xml_start_tag("c:dateAx")
+
+        self._write_axis_id(axis_ids[0])
+
+        # Write the c:scaling element.
+        self._write_scaling(
+            x_axis.get("reverse"),
+            x_axis.get("min"),
+            x_axis.get("max"),
+            x_axis.get("log_base"),
+        )
+
+        if not x_axis.get("visible"):
+            self._write_delete(1)
+
+        # Write the c:axPos element.
+        self._write_axis_pos(position, y_axis.get("reverse"))
+
+        # Write the c:majorGridlines element.
+        self._write_major_gridlines(x_axis.get("major_gridlines"))
+
+        # Write the c:minorGridlines element.
+        self._write_minor_gridlines(x_axis.get("minor_gridlines"))
+
+        # Write the axis title elements.
+        if x_axis["formula"] is not None:
+            self._write_title_formula(
+                x_axis["formula"],
+                x_axis["data_id"],
+                None,
+                x_axis["name_font"],
+                x_axis["name_layout"],
+            )
+        elif x_axis["name"] is not None:
+            self._write_title_rich(
+                x_axis["name"], None, x_axis["name_font"], x_axis["name_layout"]
+            )
+
+        # Write the c:numFmt element.
+        self._write_number_format(x_axis)
+
+        # Write the c:majorTickMark element.
+        self._write_major_tick_mark(x_axis.get("major_tick_mark"))
+
+        # Write the c:minorTickMark element.
+        self._write_minor_tick_mark(x_axis.get("minor_tick_mark"))
+
+        # Write the c:tickLblPos element.
+        self._write_tick_label_pos(x_axis.get("label_position"))
+
+        # Write the c:spPr element for the axis line.
+        self._write_sp_pr(x_axis)
+
+        # Write the axis font elements.
+        self._write_axis_font(x_axis.get("num_font"))
+
+        # Write the c:crossAx element.
+        self._write_cross_axis(axis_ids[1])
+
+        if self.show_crosses or x_axis.get("visible"):
+            # Note, the category crossing comes from the value axis.
+            if (
+                y_axis.get("crossing") is None
+                or y_axis.get("crossing") == "max"
+                or y_axis["crossing"] == "min"
+            ):
+                # Write the c:crosses element.
+                self._write_crosses(y_axis.get("crossing"))
+            else:
+                # Write the c:crossesAt element.
+                self._write_c_crosses_at(y_axis.get("crossing"))
+
+        # Write the c:auto element.
+        self._write_auto(1)
+
+        # Write the c:labelOffset element.
+        self._write_label_offset(100)
+
+        # Write the c:tickLblSkip element.
+        self._write_c_tick_lbl_skip(x_axis.get("interval_unit"))
+
+        # Write the c:tickMarkSkip element.
+        self._write_c_tick_mark_skip(x_axis.get("interval_tick"))
+
+        # Write the c:majorUnit element.
+        self._write_c_major_unit(x_axis.get("major_unit"))
+
+        # Write the c:majorTimeUnit element.
+        if x_axis.get("major_unit"):
+            self._write_c_major_time_unit(x_axis["major_unit_type"])
+
+        # Write the c:minorUnit element.
+        self._write_c_minor_unit(x_axis.get("minor_unit"))
+
+        # Write the c:minorTimeUnit element.
+        if x_axis.get("minor_unit"):
+            self._write_c_minor_time_unit(x_axis["minor_unit_type"])
+
+        self._xml_end_tag("c:dateAx")
+
+    def _write_scaling(self, reverse, min_val, max_val, log_base):
+        # Write the <c:scaling> element.
+
+        self._xml_start_tag("c:scaling")
+
+        # Write the c:logBase element.
+        self._write_c_log_base(log_base)
+
+        # Write the c:orientation element.
+        self._write_orientation(reverse)
+
+        # Write the c:max element.
+        self._write_c_max(max_val)
+
+        # Write the c:min element.
+        self._write_c_min(min_val)
+
+        self._xml_end_tag("c:scaling")
+
+    def _write_c_log_base(self, val):
+        # Write the <c:logBase> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:logBase", attributes)
+
+    def _write_orientation(self, reverse):
+        # Write the <c:orientation> element.
+        val = "minMax"
+
+        if reverse:
+            val = "maxMin"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:orientation", attributes)
+
+    def _write_c_max(self, max_val):
+        # Write the <c:max> element.
+
+        if max_val is None:
+            return
+
+        attributes = [("val", max_val)]
+
+        self._xml_empty_tag("c:max", attributes)
+
+    def _write_c_min(self, min_val):
+        # Write the <c:min> element.
+
+        if min_val is None:
+            return
+
+        attributes = [("val", min_val)]
+
+        self._xml_empty_tag("c:min", attributes)
+
+    def _write_axis_pos(self, val, reverse):
+        # Write the <c:axPos> element.
+
+        if reverse:
+            if val == "l":
+                val = "r"
+            if val == "b":
+                val = "t"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:axPos", attributes)
+
+    def _write_number_format(self, axis):
+        # Write the <c:numberFormat> element. Note: It is assumed that if
+        # a user defined number format is supplied (i.e., non-default) then
+        # the sourceLinked attribute is 0.
+        # The user can override this if required.
+        format_code = axis.get("num_format")
+        source_linked = 1
+
+        # Check if a user defined number format has been set.
+        if format_code is not None and format_code != axis["defaults"]["num_format"]:
+            source_linked = 0
+
+        # User override of sourceLinked.
+        if axis.get("num_format_linked"):
+            source_linked = 1
+
+        attributes = [
+            ("formatCode", format_code),
+            ("sourceLinked", source_linked),
+        ]
+
+        self._xml_empty_tag("c:numFmt", attributes)
+
+    def _write_cat_number_format(self, axis):
+        # Write the <c:numFmt> element. Special case handler for category
+        # axes which don't always have a number format.
+        format_code = axis.get("num_format")
+        source_linked = 1
+        default_format = 1
+
+        # Check if a user defined number format has been set.
+        if format_code is not None and format_code != axis["defaults"]["num_format"]:
+            source_linked = 0
+            default_format = 0
+
+        # User override of sourceLinked.
+        if axis.get("num_format_linked"):
+            source_linked = 1
+
+        # Skip if cat doesn't have a num format (unless it is non-default).
+        if not self.cat_has_num_fmt and default_format:
+            return
+
+        attributes = [
+            ("formatCode", format_code),
+            ("sourceLinked", source_linked),
+        ]
+
+        self._xml_empty_tag("c:numFmt", attributes)
+
+    def _write_data_label_number_format(self, format_code):
+        # Write the <c:numberFormat> element for data labels.
+        source_linked = 0
+
+        attributes = [
+            ("formatCode", format_code),
+            ("sourceLinked", source_linked),
+        ]
+
+        self._xml_empty_tag("c:numFmt", attributes)
+
+    def _write_major_tick_mark(self, val):
+        # Write the <c:majorTickMark> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:majorTickMark", attributes)
+
+    def _write_minor_tick_mark(self, val):
+        # Write the <c:minorTickMark> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:minorTickMark", attributes)
+
+    def _write_tick_label_pos(self, val=None):
+        # Write the <c:tickLblPos> element.
+        if val is None or val == "next_to":
+            val = "nextTo"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:tickLblPos", attributes)
+
+    def _write_cross_axis(self, val):
+        # Write the <c:crossAx> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:crossAx", attributes)
+
+    def _write_crosses(self, val=None):
+        # Write the <c:crosses> element.
+        if val is None:
+            val = "autoZero"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:crosses", attributes)
+
+    def _write_c_crosses_at(self, val):
+        # Write the <c:crossesAt> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:crossesAt", attributes)
+
+    def _write_auto(self, val):
+        # Write the <c:auto> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:auto", attributes)
+
+    def _write_label_align(self, val=None):
+        # Write the <c:labelAlign> element.
+
+        if val is None:
+            val = "ctr"
+
+        if val == "right":
+            val = "r"
+
+        if val == "left":
+            val = "l"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:lblAlgn", attributes)
+
+    def _write_label_offset(self, val):
+        # Write the <c:labelOffset> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:lblOffset", attributes)
+
+    def _write_c_tick_lbl_skip(self, val):
+        # Write the <c:tickLblSkip> element.
+        if val is None:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:tickLblSkip", attributes)
+
+    def _write_c_tick_mark_skip(self, val):
+        # Write the <c:tickMarkSkip> element.
+        if val is None:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:tickMarkSkip", attributes)
+
+    def _write_major_gridlines(self, gridlines):
+        # Write the <c:majorGridlines> element.
+
+        if not gridlines:
+            return
+
+        if not gridlines["visible"]:
+            return
+
+        if gridlines["line"]["defined"]:
+            self._xml_start_tag("c:majorGridlines")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(gridlines)
+
+            self._xml_end_tag("c:majorGridlines")
+        else:
+            self._xml_empty_tag("c:majorGridlines")
+
+    def _write_minor_gridlines(self, gridlines):
+        # Write the <c:minorGridlines> element.
+
+        if not gridlines:
+            return
+
+        if not gridlines["visible"]:
+            return
+
+        if gridlines["line"]["defined"]:
+            self._xml_start_tag("c:minorGridlines")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(gridlines)
+
+            self._xml_end_tag("c:minorGridlines")
+        else:
+            self._xml_empty_tag("c:minorGridlines")
+
+    def _write_cross_between(self, val):
+        # Write the <c:crossBetween> element.
+        if val is None:
+            val = self.cross_between
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:crossBetween", attributes)
+
+    def _write_c_major_unit(self, val):
+        # Write the <c:majorUnit> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:majorUnit", attributes)
+
+    def _write_c_minor_unit(self, val):
+        # Write the <c:minorUnit> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:minorUnit", attributes)
+
+    def _write_c_major_time_unit(self, val=None):
+        # Write the <c:majorTimeUnit> element.
+        if val is None:
+            val = "days"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:majorTimeUnit", attributes)
+
+    def _write_c_minor_time_unit(self, val=None):
+        # Write the <c:minorTimeUnit> element.
+        if val is None:
+            val = "days"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:minorTimeUnit", attributes)
+
+    def _write_legend(self):
+        # Write the <c:legend> element.
+        legend = self.legend
+        position = legend.get("position", "right")
+        font = legend.get("font")
+        delete_series = []
+        overlay = 0
+
+        if legend.get("delete_series") and isinstance(legend["delete_series"], list):
+            delete_series = legend["delete_series"]
+
+        if position.startswith("overlay_"):
+            position = position.replace("overlay_", "")
+            overlay = 1
+
+        allowed = {
+            "right": "r",
+            "left": "l",
+            "top": "t",
+            "bottom": "b",
+            "top_right": "tr",
+        }
+
+        if position == "none":
+            return
+
+        if position not in allowed:
+            return
+
+        position = allowed[position]
+
+        self._xml_start_tag("c:legend")
+
+        # Write the c:legendPos element.
+        self._write_legend_pos(position)
+
+        # Remove series labels from the legend.
+        for index in delete_series:
+            # Write the c:legendEntry element.
+            self._write_legend_entry(index)
+
+        # Write the c:layout element.
+        self._write_layout(legend.get("layout"), "legend")
+
+        # Write the c:overlay element.
+        if overlay:
+            self._write_overlay()
+
+        if font:
+            self._write_tx_pr(font)
+
+        # Write the c:spPr element.
+        self._write_sp_pr(legend)
+
+        self._xml_end_tag("c:legend")
+
+    def _write_legend_pos(self, val):
+        # Write the <c:legendPos> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:legendPos", attributes)
+
+    def _write_legend_entry(self, index):
+        # Write the <c:legendEntry> element.
+
+        self._xml_start_tag("c:legendEntry")
+
+        # Write the c:idx element.
+        self._write_idx(index)
+
+        # Write the c:delete element.
+        self._write_delete(1)
+
+        self._xml_end_tag("c:legendEntry")
+
+    def _write_overlay(self):
+        # Write the <c:overlay> element.
+        val = 1
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:overlay", attributes)
+
+    def _write_plot_vis_only(self):
+        # Write the <c:plotVisOnly> element.
+        val = 1
+
+        # Ignore this element if we are plotting hidden data.
+        if self.show_hidden:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:plotVisOnly", attributes)
+
+    def _write_print_settings(self):
+        # Write the <c:printSettings> element.
+        self._xml_start_tag("c:printSettings")
+
+        # Write the c:headerFooter element.
+        self._write_header_footer()
+
+        # Write the c:pageMargins element.
+        self._write_page_margins()
+
+        # Write the c:pageSetup element.
+        self._write_page_setup()
+
+        self._xml_end_tag("c:printSettings")
+
+    def _write_header_footer(self):
+        # Write the <c:headerFooter> element.
+        self._xml_empty_tag("c:headerFooter")
+
+    def _write_page_margins(self):
+        # Write the <c:pageMargins> element.
+        bottom = 0.75
+        left = 0.7
+        right = 0.7
+        top = 0.75
+        header = 0.3
+        footer = 0.3
+
+        attributes = [
+            ("b", bottom),
+            ("l", left),
+            ("r", right),
+            ("t", top),
+            ("header", header),
+            ("footer", footer),
+        ]
+
+        self._xml_empty_tag("c:pageMargins", attributes)
+
+    def _write_page_setup(self):
+        # Write the <c:pageSetup> element.
+        self._xml_empty_tag("c:pageSetup")
+
+    def _write_c_auto_title_deleted(self):
+        # Write the <c:autoTitleDeleted> element.
+        self._xml_empty_tag("c:autoTitleDeleted", [("val", 1)])
+
+    def _write_title_rich(self, title, is_y_axis, font, layout, overlay=False):
+        # Write the <c:title> element for a rich string.
+
+        self._xml_start_tag("c:title")
+
+        # Write the c:tx element.
+        self._write_tx_rich(title, is_y_axis, font)
+
+        # Write the c:layout element.
+        self._write_layout(layout, "text")
+
+        # Write the c:overlay element.
+        if overlay:
+            self._write_overlay()
+
+        self._xml_end_tag("c:title")
+
+    def _write_title_formula(
+        self, title, data_id, is_y_axis, font, layout, overlay=False
+    ):
+        # Write the <c:title> element for a rich string.
+
+        self._xml_start_tag("c:title")
+
+        # Write the c:tx element.
+        self._write_tx_formula(title, data_id)
+
+        # Write the c:layout element.
+        self._write_layout(layout, "text")
+
+        # Write the c:overlay element.
+        if overlay:
+            self._write_overlay()
+
+        # Write the c:txPr element.
+        self._write_tx_pr(font, is_y_axis)
+
+        self._xml_end_tag("c:title")
+
+    def _write_tx_rich(self, title, is_y_axis, font):
+        # Write the <c:tx> element.
+
+        self._xml_start_tag("c:tx")
+
+        # Write the c:rich element.
+        self._write_rich(title, font, is_y_axis, ignore_rich_pr=False)
+
+        self._xml_end_tag("c:tx")
+
+    def _write_tx_value(self, title):
+        # Write the <c:tx> element with a value such as for series names.
+
+        self._xml_start_tag("c:tx")
+
+        # Write the c:v element.
+        self._write_v(title)
+
+        self._xml_end_tag("c:tx")
+
+    def _write_tx_formula(self, title, data_id):
+        # Write the <c:tx> element.
+        data = None
+
+        if data_id is not None:
+            data = self.formula_data[data_id]
+
+        self._xml_start_tag("c:tx")
+
+        # Write the c:strRef element.
+        self._write_str_ref(title, data, "str")
+
+        self._xml_end_tag("c:tx")
+
+    def _write_rich(self, title, font, is_y_axis, ignore_rich_pr):
+        # Write the <c:rich> element.
+
+        if font and font.get("rotation") is not None:
+            rotation = font["rotation"]
+        else:
+            rotation = None
+
+        self._xml_start_tag("c:rich")
+
+        # Write the a:bodyPr element.
+        self._write_a_body_pr(rotation, is_y_axis)
+
+        # Write the a:lstStyle element.
+        self._write_a_lst_style()
+
+        # Write the a:p element.
+        self._write_a_p_rich(title, font, ignore_rich_pr)
+
+        self._xml_end_tag("c:rich")
+
+    def _write_a_body_pr(self, rotation, is_y_axis):
+        # Write the <a:bodyPr> element.
+        attributes = []
+
+        if rotation is None and is_y_axis:
+            rotation = -5400000
+
+        if rotation is not None:
+            if rotation == 16200000:
+                # 270 deg/stacked angle.
+                attributes.append(("rot", 0))
+                attributes.append(("vert", "wordArtVert"))
+            elif rotation == 16260000:
+                # 271 deg/East Asian vertical.
+                attributes.append(("rot", 0))
+                attributes.append(("vert", "eaVert"))
+            else:
+                attributes.append(("rot", rotation))
+                attributes.append(("vert", "horz"))
+
+        self._xml_empty_tag("a:bodyPr", attributes)
+
+    def _write_a_lst_style(self):
+        # Write the <a:lstStyle> element.
+        self._xml_empty_tag("a:lstStyle")
+
+    def _write_a_p_rich(self, title, font, ignore_rich_pr):
+        # Write the <a:p> element for rich string titles.
+
+        self._xml_start_tag("a:p")
+
+        # Write the a:pPr element.
+        if not ignore_rich_pr:
+            self._write_a_p_pr_rich(font)
+
+        # Write the a:r element.
+        self._write_a_r(title, font)
+
+        self._xml_end_tag("a:p")
+
+    def _write_a_p_formula(self, font):
+        # Write the <a:p> element for formula titles.
+
+        self._xml_start_tag("a:p")
+
+        # Write the a:pPr element.
+        self._write_a_p_pr_rich(font)
+
+        # Write the a:endParaRPr element.
+        self._write_a_end_para_rpr()
+
+        self._xml_end_tag("a:p")
+
+    def _write_a_p_pr_rich(self, font):
+        # Write the <a:pPr> element for rich string titles.
+
+        self._xml_start_tag("a:pPr")
+
+        # Write the a:defRPr element.
+        self._write_a_def_rpr(font)
+
+        self._xml_end_tag("a:pPr")
+
+    def _write_a_def_rpr(self, font):
+        # Write the <a:defRPr> element.
+        has_color = 0
+
+        style_attributes = Shape._get_font_style_attributes(font)
+        latin_attributes = Shape._get_font_latin_attributes(font)
+
+        if font and font.get("color") is not None:
+            has_color = 1
+
+        if latin_attributes or has_color:
+            self._xml_start_tag("a:defRPr", style_attributes)
+
+            if has_color:
+                self._write_a_solid_fill({"color": font["color"]})
+
+            if latin_attributes:
+                self._write_a_latin(latin_attributes)
+
+            self._xml_end_tag("a:defRPr")
+        else:
+            self._xml_empty_tag("a:defRPr", style_attributes)
+
+    def _write_a_end_para_rpr(self):
+        # Write the <a:endParaRPr> element.
+        lang = "en-US"
+
+        attributes = [("lang", lang)]
+
+        self._xml_empty_tag("a:endParaRPr", attributes)
+
+    def _write_a_r(self, title, font):
+        # Write the <a:r> element.
+
+        self._xml_start_tag("a:r")
+
+        # Write the a:rPr element.
+        self._write_a_r_pr(font)
+
+        # Write the a:t element.
+        self._write_a_t(title)
+
+        self._xml_end_tag("a:r")
+
+    def _write_a_r_pr(self, font):
+        # Write the <a:rPr> element.
+        has_color = 0
+        lang = "en-US"
+
+        style_attributes = Shape._get_font_style_attributes(font)
+        latin_attributes = Shape._get_font_latin_attributes(font)
+
+        if font and font["color"] is not None:
+            has_color = 1
+
+        # Add the lang type to the attributes.
+        style_attributes.insert(0, ("lang", lang))
+
+        if latin_attributes or has_color:
+            self._xml_start_tag("a:rPr", style_attributes)
+
+            if has_color:
+                self._write_a_solid_fill({"color": font["color"]})
+
+            if latin_attributes:
+                self._write_a_latin(latin_attributes)
+
+            self._xml_end_tag("a:rPr")
+        else:
+            self._xml_empty_tag("a:rPr", style_attributes)
+
+    def _write_a_t(self, title):
+        # Write the <a:t> element.
+
+        self._xml_data_element("a:t", title)
+
+    def _write_tx_pr(self, font, is_y_axis=False):
+        # Write the <c:txPr> element.
+
+        if font and font.get("rotation") is not None:
+            rotation = font["rotation"]
+        else:
+            rotation = None
+
+        self._xml_start_tag("c:txPr")
+
+        # Write the a:bodyPr element.
+        self._write_a_body_pr(rotation, is_y_axis)
+
+        # Write the a:lstStyle element.
+        self._write_a_lst_style()
+
+        # Write the a:p element.
+        self._write_a_p_formula(font)
+
+        self._xml_end_tag("c:txPr")
+
+    def _write_marker(self, marker):
+        # Write the <c:marker> element.
+        if marker is None:
+            marker = self.default_marker
+
+        if not marker:
+            return
+
+        if marker["type"] == "automatic":
+            return
+
+        self._xml_start_tag("c:marker")
+
+        # Write the c:symbol element.
+        self._write_symbol(marker["type"])
+
+        # Write the c:size element.
+        if marker.get("size"):
+            self._write_marker_size(marker["size"])
+
+        # Write the c:spPr element.
+        self._write_sp_pr(marker)
+
+        self._xml_end_tag("c:marker")
+
+    def _write_marker_size(self, val):
+        # Write the <c:size> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:size", attributes)
+
+    def _write_symbol(self, val):
+        # Write the <c:symbol> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:symbol", attributes)
+
+    def _write_sp_pr(self, series):
+        # Write the <c:spPr> element.
+
+        if not self._has_fill_formatting(series):
+            return
+
+        self._xml_start_tag("c:spPr")
+
+        # Write the fill elements for solid charts such as pie and bar.
+        if series.get("fill") and series["fill"]["defined"]:
+            if "none" in series["fill"]:
+                # Write the a:noFill element.
+                self._write_a_no_fill()
+            else:
+                # Write the a:solidFill element.
+                self._write_a_solid_fill(series["fill"])
+
+        if series.get("pattern"):
+            # Write the a:gradFill element.
+            self._write_a_patt_fill(series["pattern"])
+
+        if series.get("gradient"):
+            # Write the a:gradFill element.
+            self._write_a_grad_fill(series["gradient"])
+
+        # Write the a:ln element.
+        if series.get("line") and series["line"]["defined"]:
+            self._write_a_ln(series["line"])
+
+        self._xml_end_tag("c:spPr")
+
+    def _write_a_ln(self, line):
+        # Write the <a:ln> element.
+        attributes = []
+
+        # Add the line width as an attribute.
+        width = line.get("width")
+
+        if width is not None:
+            # Round width to nearest 0.25, like Excel.
+            width = int((width + 0.125) * 4) / 4.0
+
+            # Convert to internal units.
+            width = int(0.5 + (12700 * width))
+
+            attributes = [("w", width)]
+
+        if line.get("none") or line.get("color") or line.get("dash_type"):
+            self._xml_start_tag("a:ln", attributes)
+
+            # Write the line fill.
+            if "none" in line:
+                # Write the a:noFill element.
+                self._write_a_no_fill()
+            elif "color" in line:
+                # Write the a:solidFill element.
+                self._write_a_solid_fill(line)
+
+            # Write the line/dash type.
+            line_type = line.get("dash_type")
+            if line_type:
+                # Write the a:prstDash element.
+                self._write_a_prst_dash(line_type)
+
+            self._xml_end_tag("a:ln")
+        else:
+            self._xml_empty_tag("a:ln", attributes)
+
+    def _write_a_no_fill(self):
+        # Write the <a:noFill> element.
+        self._xml_empty_tag("a:noFill")
+
+    def _write_a_solid_fill(self, fill):
+        # Write the <a:solidFill> element.
+
+        self._xml_start_tag("a:solidFill")
+
+        if "color" in fill:
+            color = _get_rgb_color(fill["color"])
+            transparency = fill.get("transparency")
+            # Write the a:srgbClr element.
+            self._write_a_srgb_clr(color, transparency)
+
+        self._xml_end_tag("a:solidFill")
+
+    def _write_a_srgb_clr(self, val, transparency=None):
+        # Write the <a:srgbClr> element.
+        attributes = [("val", val)]
+
+        if transparency:
+            self._xml_start_tag("a:srgbClr", attributes)
+
+            # Write the a:alpha element.
+            self._write_a_alpha(transparency)
+
+            self._xml_end_tag("a:srgbClr")
+        else:
+            self._xml_empty_tag("a:srgbClr", attributes)
+
+    def _write_a_alpha(self, val):
+        # Write the <a:alpha> element.
+
+        val = int((100 - int(val)) * 1000)
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("a:alpha", attributes)
+
+    def _write_a_prst_dash(self, val):
+        # Write the <a:prstDash> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("a:prstDash", attributes)
+
+    def _write_trendline(self, trendline):
+        # Write the <c:trendline> element.
+
+        if not trendline:
+            return
+
+        self._xml_start_tag("c:trendline")
+
+        # Write the c:name element.
+        self._write_name(trendline.get("name"))
+
+        # Write the c:spPr element.
+        self._write_sp_pr(trendline)
+
+        # Write the c:trendlineType element.
+        self._write_trendline_type(trendline["type"])
+
+        # Write the c:order element for polynomial trendlines.
+        if trendline["type"] == "poly":
+            self._write_trendline_order(trendline.get("order"))
+
+        # Write the c:period element for moving average trendlines.
+        if trendline["type"] == "movingAvg":
+            self._write_period(trendline.get("period"))
+
+        # Write the c:forward element.
+        self._write_forward(trendline.get("forward"))
+
+        # Write the c:backward element.
+        self._write_backward(trendline.get("backward"))
+
+        if "intercept" in trendline:
+            # Write the c:intercept element.
+            self._write_c_intercept(trendline["intercept"])
+
+        if trendline.get("display_r_squared"):
+            # Write the c:dispRSqr element.
+            self._write_c_disp_rsqr()
+
+        if trendline.get("display_equation"):
+            # Write the c:dispEq element.
+            self._write_c_disp_eq()
+
+            # Write the c:trendlineLbl element.
+            self._write_c_trendline_lbl(trendline)
+
+        self._xml_end_tag("c:trendline")
+
+    def _write_trendline_type(self, val):
+        # Write the <c:trendlineType> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:trendlineType", attributes)
+
+    def _write_name(self, data):
+        # Write the <c:name> element.
+
+        if data is None:
+            return
+
+        self._xml_data_element("c:name", data)
+
+    def _write_trendline_order(self, val):
+        # Write the <c:order> element.
+        val = max(val, 2)
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:order", attributes)
+
+    def _write_period(self, val):
+        # Write the <c:period> element.
+        val = max(val, 2)
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:period", attributes)
+
+    def _write_forward(self, val):
+        # Write the <c:forward> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:forward", attributes)
+
+    def _write_backward(self, val):
+        # Write the <c:backward> element.
+
+        if not val:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:backward", attributes)
+
+    def _write_c_intercept(self, val):
+        # Write the <c:intercept> element.
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:intercept", attributes)
+
+    def _write_c_disp_eq(self):
+        # Write the <c:dispEq> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:dispEq", attributes)
+
+    def _write_c_disp_rsqr(self):
+        # Write the <c:dispRSqr> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:dispRSqr", attributes)
+
+    def _write_c_trendline_lbl(self, trendline):
+        # Write the <c:trendlineLbl> element.
+        self._xml_start_tag("c:trendlineLbl")
+
+        # Write the c:layout element.
+        self._write_layout(None, None)
+
+        # Write the c:numFmt element.
+        self._write_trendline_num_fmt()
+
+        # Write the c:spPr element.
+        self._write_sp_pr(trendline["label"])
+
+        # Write the data label font elements.
+        if trendline["label"]:
+            font = trendline["label"].get("font")
+            if font:
+                self._write_axis_font(font)
+
+        self._xml_end_tag("c:trendlineLbl")
+
+    def _write_trendline_num_fmt(self):
+        # Write the <c:numFmt> element.
+        attributes = [
+            ("formatCode", "General"),
+            ("sourceLinked", 0),
+        ]
+
+        self._xml_empty_tag("c:numFmt", attributes)
+
+    def _write_hi_low_lines(self):
+        # Write the <c:hiLowLines> element.
+        hi_low_lines = self.hi_low_lines
+
+        if hi_low_lines is None:
+            return
+
+        if "line" in hi_low_lines and hi_low_lines["line"]["defined"]:
+            self._xml_start_tag("c:hiLowLines")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(hi_low_lines)
+
+            self._xml_end_tag("c:hiLowLines")
+        else:
+            self._xml_empty_tag("c:hiLowLines")
+
+    def _write_drop_lines(self):
+        # Write the <c:dropLines> element.
+        drop_lines = self.drop_lines
+
+        if drop_lines is None:
+            return
+
+        if drop_lines["line"]["defined"]:
+            self._xml_start_tag("c:dropLines")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(drop_lines)
+
+            self._xml_end_tag("c:dropLines")
+        else:
+            self._xml_empty_tag("c:dropLines")
+
+    def _write_overlap(self, val):
+        # Write the <c:overlap> element.
+
+        if val is None:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:overlap", attributes)
+
+    def _write_num_cache(self, data):
+        # Write the <c:numCache> element.
+        if data:
+            count = len(data)
+        else:
+            count = 0
+
+        self._xml_start_tag("c:numCache")
+
+        # Write the c:formatCode element.
+        self._write_format_code("General")
+
+        # Write the c:ptCount element.
+        self._write_pt_count(count)
+
+        for i in range(count):
+            token = data[i]
+
+            if token is None:
+                continue
+
+            try:
+                float(token)
+            except ValueError:
+                # Write non-numeric data as 0.
+                token = 0
+
+            # Write the c:pt element.
+            self._write_pt(i, token)
+
+        self._xml_end_tag("c:numCache")
+
+    def _write_str_cache(self, data):
+        # Write the <c:strCache> element.
+        count = len(data)
+
+        self._xml_start_tag("c:strCache")
+
+        # Write the c:ptCount element.
+        self._write_pt_count(count)
+
+        for i in range(count):
+            # Write the c:pt element.
+            self._write_pt(i, data[i])
+
+        self._xml_end_tag("c:strCache")
+
+    def _write_format_code(self, data):
+        # Write the <c:formatCode> element.
+
+        self._xml_data_element("c:formatCode", data)
+
+    def _write_pt_count(self, val):
+        # Write the <c:ptCount> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:ptCount", attributes)
+
+    def _write_pt(self, idx, value):
+        # Write the <c:pt> element.
+
+        if value is None:
+            return
+
+        attributes = [("idx", idx)]
+
+        self._xml_start_tag("c:pt", attributes)
+
+        # Write the c:v element.
+        self._write_v(value)
+
+        self._xml_end_tag("c:pt")
+
+    def _write_v(self, data):
+        # Write the <c:v> element.
+
+        self._xml_data_element("c:v", data)
+
+    def _write_protection(self):
+        # Write the <c:protection> element.
+        if not self.protection:
+            return
+
+        self._xml_empty_tag("c:protection")
+
+    def _write_d_pt(self, points):
+        # Write the <c:dPt> elements.
+        index = -1
+
+        if not points:
+            return
+
+        for point in points:
+            index += 1
+            if not point:
+                continue
+
+            self._write_d_pt_point(index, point)
+
+    def _write_d_pt_point(self, index, point):
+        # Write an individual <c:dPt> element.
+
+        self._xml_start_tag("c:dPt")
+
+        # Write the c:idx element.
+        self._write_idx(index)
+
+        # Write the c:spPr element.
+        self._write_sp_pr(point)
+
+        self._xml_end_tag("c:dPt")
+
+    def _write_d_lbls(self, labels):
+        # Write the <c:dLbls> element.
+
+        if not labels:
+            return
+
+        self._xml_start_tag("c:dLbls")
+
+        # Write the custom c:dLbl elements.
+        if labels.get("custom"):
+            self._write_custom_labels(labels, labels["custom"])
+
+        # Write the c:numFmt element.
+        if labels.get("num_format"):
+            self._write_data_label_number_format(labels["num_format"])
+
+        # Write the c:spPr element for the plotarea formatting.
+        self._write_sp_pr(labels)
+
+        # Write the data label font elements.
+        if labels.get("font"):
+            self._write_axis_font(labels["font"])
+
+        # Write the c:dLblPos element.
+        if labels.get("position"):
+            self._write_d_lbl_pos(labels["position"])
+
+        # Write the c:showLegendKey element.
+        if labels.get("legend_key"):
+            self._write_show_legend_key()
+
+        # Write the c:showVal element.
+        if labels.get("value"):
+            self._write_show_val()
+
+        # Write the c:showCatName element.
+        if labels.get("category"):
+            self._write_show_cat_name()
+
+        # Write the c:showSerName element.
+        if labels.get("series_name"):
+            self._write_show_ser_name()
+
+        # Write the c:showPercent element.
+        if labels.get("percentage"):
+            self._write_show_percent()
+
+        # Write the c:separator element.
+        if labels.get("separator"):
+            self._write_separator(labels["separator"])
+
+        # Write the c:showLeaderLines element.
+        if labels.get("leader_lines"):
+            self._write_show_leader_lines()
+
+        self._xml_end_tag("c:dLbls")
+
+    def _write_custom_labels(self, parent, labels):
+        # Write the <c:showLegendKey> element.
+        index = 0
+
+        for label in labels:
+            index += 1
+
+            if label is None:
+                continue
+
+            self._xml_start_tag("c:dLbl")
+
+            # Write the c:idx element.
+            self._write_idx(index - 1)
+
+            delete_label = label.get("delete")
+
+            if delete_label:
+                self._write_delete(1)
+
+            elif label.get("formula"):
+                self._write_custom_label_formula(label)
+
+                if parent.get("position"):
+                    self._write_d_lbl_pos(parent["position"])
+
+                if parent.get("value"):
+                    self._write_show_val()
+                if parent.get("category"):
+                    self._write_show_cat_name()
+                if parent.get("series_name"):
+                    self._write_show_ser_name()
+
+            elif label.get("value"):
+                self._write_custom_label_str(label)
+
+                if parent.get("position"):
+                    self._write_d_lbl_pos(parent["position"])
+
+                if parent.get("value"):
+                    self._write_show_val()
+                if parent.get("category"):
+                    self._write_show_cat_name()
+                if parent.get("series_name"):
+                    self._write_show_ser_name()
+            else:
+                self._write_custom_label_format_only(label)
+
+            self._xml_end_tag("c:dLbl")
+
+    def _write_custom_label_str(self, label):
+        # Write parts of the <c:dLbl> element for strings.
+        title = label.get("value")
+        font = label.get("font")
+        has_formatting = self._has_fill_formatting(label)
+
+        # Write the c:layout element.
+        self._write_layout(None, None)
+
+        self._xml_start_tag("c:tx")
+
+        # Write the c:rich element.
+        self._write_rich(title, font, False, not has_formatting)
+
+        self._xml_end_tag("c:tx")
+
+        # Write the c:spPr element.
+        self._write_sp_pr(label)
+
+    def _write_custom_label_formula(self, label):
+        # Write parts of the <c:dLbl> element for formulas.
+        formula = label.get("formula")
+        data_id = label.get("data_id")
+        data = None
+
+        if data_id is not None:
+            data = self.formula_data[data_id]
+
+        # Write the c:layout element.
+        self._write_layout(None, None)
+
+        self._xml_start_tag("c:tx")
+
+        # Write the c:strRef element.
+        self._write_str_ref(formula, data, "str")
+
+        self._xml_end_tag("c:tx")
+
+        # Write the data label formatting, if any.
+        self._write_custom_label_format_only(label)
+
+    def _write_custom_label_format_only(self, label):
+        # Write parts of the <c:dLbl> labels with changed formatting.
+        font = label.get("font")
+        has_formatting = self._has_fill_formatting(label)
+
+        if has_formatting:
+            self._write_sp_pr(label)
+            self._write_tx_pr(font)
+        elif font:
+            self._xml_empty_tag("c:spPr")
+            self._write_tx_pr(font)
+
+    def _write_show_legend_key(self):
+        # Write the <c:showLegendKey> element.
+        val = "1"
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:showLegendKey", attributes)
+
+    def _write_show_val(self):
+        # Write the <c:showVal> element.
+        val = 1
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:showVal", attributes)
+
+    def _write_show_cat_name(self):
+        # Write the <c:showCatName> element.
+        val = 1
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:showCatName", attributes)
+
+    def _write_show_ser_name(self):
+        # Write the <c:showSerName> element.
+        val = 1
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:showSerName", attributes)
+
+    def _write_show_percent(self):
+        # Write the <c:showPercent> element.
+        val = 1
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:showPercent", attributes)
+
+    def _write_separator(self, data):
+        # Write the <c:separator> element.
+        self._xml_data_element("c:separator", data)
+
+    def _write_show_leader_lines(self):
+        # Write the <c:showLeaderLines> element.
+        #
+        # This is different for Pie/Doughnut charts. Other chart types only
+        # supported leader lines after Excel 2015 via an extension element.
+        #
+        uri = "{CE6537A1-D6FC-4f65-9D91-7224C49458BB}"
+        xmlns_c_15 = "http://schemas.microsoft.com/office/drawing/2012/chart"
+
+        attributes = [
+            ("uri", uri),
+            ("xmlns:c15", xmlns_c_15),
+        ]
+
+        self._xml_start_tag("c:extLst")
+        self._xml_start_tag("c:ext", attributes)
+        self._xml_empty_tag("c15:showLeaderLines", [("val", 1)])
+        self._xml_end_tag("c:ext")
+        self._xml_end_tag("c:extLst")
+
+    def _write_d_lbl_pos(self, val):
+        # Write the <c:dLblPos> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:dLblPos", attributes)
+
+    def _write_delete(self, val):
+        # Write the <c:delete> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:delete", attributes)
+
+    def _write_c_invert_if_negative(self, invert):
+        # Write the <c:invertIfNegative> element.
+        val = 1
+
+        if not invert:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:invertIfNegative", attributes)
+
+    def _write_axis_font(self, font):
+        # Write the axis font elements.
+
+        if not font:
+            return
+
+        self._xml_start_tag("c:txPr")
+        self._write_a_body_pr(font.get("rotation"), None)
+        self._write_a_lst_style()
+        self._xml_start_tag("a:p")
+
+        self._write_a_p_pr_rich(font)
+
+        self._write_a_end_para_rpr()
+        self._xml_end_tag("a:p")
+        self._xml_end_tag("c:txPr")
+
+    def _write_a_latin(self, attributes):
+        # Write the <a:latin> element.
+        self._xml_empty_tag("a:latin", attributes)
+
+    def _write_d_table(self):
+        # Write the <c:dTable> element.
+        table = self.table
+
+        if not table:
+            return
+
+        self._xml_start_tag("c:dTable")
+
+        if table["horizontal"]:
+            # Write the c:showHorzBorder element.
+            self._write_show_horz_border()
+
+        if table["vertical"]:
+            # Write the c:showVertBorder element.
+            self._write_show_vert_border()
+
+        if table["outline"]:
+            # Write the c:showOutline element.
+            self._write_show_outline()
+
+        if table["show_keys"]:
+            # Write the c:showKeys element.
+            self._write_show_keys()
+
+        if table["font"]:
+            # Write the table font.
+            self._write_tx_pr(table["font"])
+
+        self._xml_end_tag("c:dTable")
+
+    def _write_show_horz_border(self):
+        # Write the <c:showHorzBorder> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:showHorzBorder", attributes)
+
+    def _write_show_vert_border(self):
+        # Write the <c:showVertBorder> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:showVertBorder", attributes)
+
+    def _write_show_outline(self):
+        # Write the <c:showOutline> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:showOutline", attributes)
+
+    def _write_show_keys(self):
+        # Write the <c:showKeys> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:showKeys", attributes)
+
+    def _write_error_bars(self, error_bars):
+        # Write the X and Y error bars.
+
+        if not error_bars:
+            return
+
+        if error_bars["x_error_bars"]:
+            self._write_err_bars("x", error_bars["x_error_bars"])
+
+        if error_bars["y_error_bars"]:
+            self._write_err_bars("y", error_bars["y_error_bars"])
+
+    def _write_err_bars(self, direction, error_bars):
+        # Write the <c:errBars> element.
+
+        if not error_bars:
+            return
+
+        self._xml_start_tag("c:errBars")
+
+        # Write the c:errDir element.
+        self._write_err_dir(direction)
+
+        # Write the c:errBarType element.
+        self._write_err_bar_type(error_bars["direction"])
+
+        # Write the c:errValType element.
+        self._write_err_val_type(error_bars["type"])
+
+        if not error_bars["endcap"]:
+            # Write the c:noEndCap element.
+            self._write_no_end_cap()
+
+        if error_bars["type"] == "stdErr":
+            # Don't need to write a c:errValType tag.
+            pass
+        elif error_bars["type"] == "cust":
+            # Write the custom error tags.
+            self._write_custom_error(error_bars)
+        else:
+            # Write the c:val element.
+            self._write_error_val(error_bars["value"])
+
+        # Write the c:spPr element.
+        self._write_sp_pr(error_bars)
+
+        self._xml_end_tag("c:errBars")
+
+    def _write_err_dir(self, val):
+        # Write the <c:errDir> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:errDir", attributes)
+
+    def _write_err_bar_type(self, val):
+        # Write the <c:errBarType> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:errBarType", attributes)
+
+    def _write_err_val_type(self, val):
+        # Write the <c:errValType> element.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:errValType", attributes)
+
+    def _write_no_end_cap(self):
+        # Write the <c:noEndCap> element.
+        attributes = [("val", 1)]
+
+        self._xml_empty_tag("c:noEndCap", attributes)
+
+    def _write_error_val(self, val):
+        # Write the <c:val> element for error bars.
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:val", attributes)
+
+    def _write_custom_error(self, error_bars):
+        # Write the custom error bars tags.
+
+        if error_bars["plus_values"]:
+            # Write the c:plus element.
+            self._xml_start_tag("c:plus")
+
+            if isinstance(error_bars["plus_values"], list):
+                self._write_num_lit(error_bars["plus_values"])
+            else:
+                self._write_num_ref(
+                    error_bars["plus_values"], error_bars["plus_data"], "num"
+                )
+            self._xml_end_tag("c:plus")
+
+        if error_bars["minus_values"]:
+            # Write the c:minus element.
+            self._xml_start_tag("c:minus")
+
+            if isinstance(error_bars["minus_values"], list):
+                self._write_num_lit(error_bars["minus_values"])
+            else:
+                self._write_num_ref(
+                    error_bars["minus_values"], error_bars["minus_data"], "num"
+                )
+            self._xml_end_tag("c:minus")
+
+    def _write_num_lit(self, data):
+        # Write the <c:numLit> element for literal number list elements.
+        count = len(data)
+
+        # Write the c:numLit element.
+        self._xml_start_tag("c:numLit")
+
+        # Write the c:formatCode element.
+        self._write_format_code("General")
+
+        # Write the c:ptCount element.
+        self._write_pt_count(count)
+
+        for i in range(count):
+            token = data[i]
+
+            if token is None:
+                continue
+
+            try:
+                float(token)
+            except ValueError:
+                # Write non-numeric data as 0.
+                token = 0
+
+            # Write the c:pt element.
+            self._write_pt(i, token)
+
+        self._xml_end_tag("c:numLit")
+
+    def _write_up_down_bars(self):
+        # Write the <c:upDownBars> element.
+        up_down_bars = self.up_down_bars
+
+        if up_down_bars is None:
+            return
+
+        self._xml_start_tag("c:upDownBars")
+
+        # Write the c:gapWidth element.
+        self._write_gap_width(150)
+
+        # Write the c:upBars element.
+        self._write_up_bars(up_down_bars.get("up"))
+
+        # Write the c:downBars element.
+        self._write_down_bars(up_down_bars.get("down"))
+
+        self._xml_end_tag("c:upDownBars")
+
+    def _write_gap_width(self, val):
+        # Write the <c:gapWidth> element.
+
+        if val is None:
+            return
+
+        attributes = [("val", val)]
+
+        self._xml_empty_tag("c:gapWidth", attributes)
+
+    def _write_up_bars(self, bar_format):
+        # Write the <c:upBars> element.
+
+        if bar_format["line"] and bar_format["line"]["defined"]:
+            self._xml_start_tag("c:upBars")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(bar_format)
+
+            self._xml_end_tag("c:upBars")
+        else:
+            self._xml_empty_tag("c:upBars")
+
+    def _write_down_bars(self, bar_format):
+        # Write the <c:downBars> element.
+
+        if bar_format["line"] and bar_format["line"]["defined"]:
+            self._xml_start_tag("c:downBars")
+
+            # Write the c:spPr element.
+            self._write_sp_pr(bar_format)
+
+            self._xml_end_tag("c:downBars")
+        else:
+            self._xml_empty_tag("c:downBars")
+
+    def _write_disp_units(self, units, display):
+        # Write the <c:dispUnits> element.
+
+        if not units:
+            return
+
+        attributes = [("val", units)]
+
+        self._xml_start_tag("c:dispUnits")
+        self._xml_empty_tag("c:builtInUnit", attributes)
+
+        if display:
+            self._xml_start_tag("c:dispUnitsLbl")
+            self._xml_empty_tag("c:layout")
+            self._xml_end_tag("c:dispUnitsLbl")
+
+        self._xml_end_tag("c:dispUnits")
+
+    def _write_a_grad_fill(self, gradient):
+        # Write the <a:gradFill> element.
+
+        attributes = [("flip", "none"), ("rotWithShape", "1")]
+
+        if gradient["type"] == "linear":
+            attributes = []
+
+        self._xml_start_tag("a:gradFill", attributes)
+
+        # Write the a:gsLst element.
+        self._write_a_gs_lst(gradient)
+
+        if gradient["type"] == "linear":
+            # Write the a:lin element.
+            self._write_a_lin(gradient["angle"])
+        else:
+            # Write the a:path element.
+            self._write_a_path(gradient["type"])
+
+            # Write the a:tileRect element.
+            self._write_a_tile_rect(gradient["type"])
+
+        self._xml_end_tag("a:gradFill")
+
+    def _write_a_gs_lst(self, gradient):
+        # Write the <a:gsLst> element.
+        positions = gradient["positions"]
+        colors = gradient["colors"]
+
+        self._xml_start_tag("a:gsLst")
+
+        for i, color in enumerate(colors):
+            pos = int(positions[i] * 1000)
+            attributes = [("pos", pos)]
+            self._xml_start_tag("a:gs", attributes)
+
+            # Write the a:srgbClr element.
+            color = _get_rgb_color(color)
+            self._write_a_srgb_clr(color)
+
+            self._xml_end_tag("a:gs")
+
+        self._xml_end_tag("a:gsLst")
+
+    def _write_a_lin(self, angle):
+        # Write the <a:lin> element.
+
+        angle = int(60000 * angle)
+
+        attributes = [
+            ("ang", angle),
+            ("scaled", "0"),
+        ]
+
+        self._xml_empty_tag("a:lin", attributes)
+
+    def _write_a_path(self, gradient_type):
+        # Write the <a:path> element.
+
+        attributes = [("path", gradient_type)]
+
+        self._xml_start_tag("a:path", attributes)
+
+        # Write the a:fillToRect element.
+        self._write_a_fill_to_rect(gradient_type)
+
+        self._xml_end_tag("a:path")
+
+    def _write_a_fill_to_rect(self, gradient_type):
+        # Write the <a:fillToRect> element.
+
+        if gradient_type == "shape":
+            attributes = [
+                ("l", "50000"),
+                ("t", "50000"),
+                ("r", "50000"),
+                ("b", "50000"),
+            ]
+        else:
+            attributes = [
+                ("l", "100000"),
+                ("t", "100000"),
+            ]
+
+        self._xml_empty_tag("a:fillToRect", attributes)
+
+    def _write_a_tile_rect(self, gradient_type):
+        # Write the <a:tileRect> element.
+
+        if gradient_type == "shape":
+            attributes = []
+        else:
+            attributes = [
+                ("r", "-100000"),
+                ("b", "-100000"),
+            ]
+
+        self._xml_empty_tag("a:tileRect", attributes)
+
+    def _write_a_patt_fill(self, pattern):
+        # Write the <a:pattFill> element.
+
+        attributes = [("prst", pattern["pattern"])]
+
+        self._xml_start_tag("a:pattFill", attributes)
+
+        # Write the a:fgClr element.
+        self._write_a_fg_clr(pattern["fg_color"])
+
+        # Write the a:bgClr element.
+        self._write_a_bg_clr(pattern["bg_color"])
+
+        self._xml_end_tag("a:pattFill")
+
+    def _write_a_fg_clr(self, color):
+        # Write the <a:fgClr> element.
+
+        color = _get_rgb_color(color)
+
+        self._xml_start_tag("a:fgClr")
+
+        # Write the a:srgbClr element.
+        self._write_a_srgb_clr(color)
+
+        self._xml_end_tag("a:fgClr")
+
+    def _write_a_bg_clr(self, color):
+        # Write the <a:bgClr> element.
+
+        color = _get_rgb_color(color)
+
+        self._xml_start_tag("a:bgClr")
+
+        # Write the a:srgbClr element.
+        self._write_a_srgb_clr(color)
+
+        self._xml_end_tag("a:bgClr")