two version of R2R are hereHEADmaster

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diff --git a/.venv/lib/python3.12/site-packages/bs4/tests/__init__.py b/.venv/lib/python3.12/site-packages/bs4/tests/__init__.py
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+# encoding: utf-8
+"""Helper classes for tests."""
+
+# Use of this source code is governed by the MIT license.
+__license__ = "MIT"
+
+import pickle
+import importlib
+import copy
+import warnings
+import pytest
+from bs4 import BeautifulSoup
+from bs4.element import (
+    AttributeValueList,
+    CharsetMetaAttributeValue,
+    Comment,
+    ContentMetaAttributeValue,
+    Doctype,
+    PageElement,
+    PYTHON_SPECIFIC_ENCODINGS,
+    Script,
+    Stylesheet,
+    Tag,
+)
+from bs4.filter import SoupStrainer
+from bs4.builder import (
+    XMLParsedAsHTMLWarning,
+)
+from bs4._typing import _IncomingMarkup
+
+from bs4.builder import TreeBuilder
+from bs4.builder._htmlparser import HTMLParserTreeBuilder
+
+from typing import (
+    Any,
+    Iterable,
+    Optional,
+    Tuple,
+    Type,
+)
+
+# Some tests depend on specific third-party libraries. We use
+# @pytest.mark.skipIf on the following conditionals to skip them
+# if the libraries are not installed.
+try:
+    from soupsieve import SelectorSyntaxError
+
+    SOUP_SIEVE_PRESENT = True
+except ImportError:
+    SOUP_SIEVE_PRESENT = False
+
+HTML5LIB_PRESENT = importlib.util.find_spec("html5lib") is not None
+
+try:
+    import lxml.etree
+    LXML_PRESENT = True
+    LXML_VERSION = lxml.etree.LXML_VERSION
+except ImportError:
+    LXML_PRESENT = False
+    LXML_VERSION = (0,)
+
+default_builder: Type[TreeBuilder] = HTMLParserTreeBuilder
+
+BAD_DOCUMENT: str = """A bare string
+<!DOCTYPE xsl:stylesheet SYSTEM "htmlent.dtd">
+<!DOCTYPE xsl:stylesheet PUBLIC "htmlent.dtd">
+<div><![CDATA[A CDATA section where it doesn't belong]]></div>
+<div><svg><![CDATA[HTML5 does allow CDATA sections in SVG]]></svg></div>
+<div>A <meta> tag</div>
+<div>A <br> tag that supposedly has contents.</br></div>
+<div>AT&T</div>
+<div><textarea>Within a textarea, markup like <b> tags and <&<&amp; should be treated as literal</textarea></div>
+<div><script>if (i < 2) { alert("<b>Markup within script tags should be treated as literal.</b>"); }</script></div>
+<div>This numeric entity is missing the final semicolon: <x t="pi&#241ata"></div>
+<div><a href="http://example.com/</a> that attribute value never got closed</div>
+<div><a href="foo</a>, </a><a href="bar">that attribute value was closed by the subsequent tag</a></div>
+<! This document starts with a bogus declaration ><div>a</div>
+<div>This document contains <!an incomplete declaration <div>(do you see it?)</div>
+<div>This document ends with <!an incomplete declaration
+<div><a style={height:21px;}>That attribute value was bogus</a></div>
+<! DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">The doctype is invalid because it contains extra whitespace
+<div><table><td nowrap>That boolean attribute had no value</td></table></div>
+<div>Here's a nonexistent entity: &#foo; (do you see it?)</div>
+<div>This document ends before the entity finishes: &gt
+<div><p>Paragraphs shouldn't contain block display elements, but this one does: <dl><dt>you see?</dt></p>
+<b b="20" a="1" b="10" a="2" a="3" a="4">Multiple values for the same attribute.</b>
+<div><table><tr><td>Here's a table</td></tr></table></div>
+<div><table id="1"><tr><td>Here's a nested table:<table id="2"><tr><td>foo</td></tr></table></td></div>
+<div>This tag contains nothing but whitespace: <b>    </b></div>
+<div><blockquote><p><b>This p tag is cut off by</blockquote></p>the end of the blockquote tag</div>
+<div><table><div>This table contains bare markup</div></table></div>
+<div><div id="1">\n <a href="link1">This link is never closed.\n</div>\n<div id="2">\n <div id="3">\n   <a href="link2">This link is closed.</a>\n  </div>\n</div></div>
+<div>This document contains a <!DOCTYPE surprise>surprise doctype</div>
+<div><a><B><Cd><EFG>Mixed case tags are folded to lowercase</efg></CD></b></A></div>
+<div><our\u2603>Tag name contains Unicode characters</our\u2603></div>
+<div><a \u2603="snowman">Attribute name contains Unicode characters</a></div>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
+"""
+
+
+class SoupTest(object):
+    @property
+    def default_builder(self) -> Type[TreeBuilder]:
+        return default_builder
+
+    def soup(self, markup: _IncomingMarkup, **kwargs: Any) -> BeautifulSoup:
+        """Build a Beautiful Soup object from markup."""
+        builder = kwargs.pop("builder", self.default_builder)
+        return BeautifulSoup(markup, builder=builder, **kwargs)
+
+    def document_for(self, markup: str, **kwargs: Any) -> str:
+        """Turn an HTML fragment into a document.
+
+        The details depend on the builder.
+        """
+        return self.default_builder(**kwargs).test_fragment_to_document(markup)
+
+    def assert_soup(
+        self, to_parse: _IncomingMarkup, compare_parsed_to: Optional[str] = None
+    ) -> None:
+        """Parse some markup using Beautiful Soup and verify that
+        the output markup is as expected.
+        """
+        builder = self.default_builder
+        obj = BeautifulSoup(to_parse, builder=builder)
+        if compare_parsed_to is None:
+            assert isinstance(to_parse, str)
+            compare_parsed_to = to_parse
+
+        # Verify that the documents come out the same.
+        assert obj.decode() == self.document_for(compare_parsed_to)
+
+        # Also run some checks on the BeautifulSoup object itself:
+
+        # Verify that every tag that was opened was eventually closed.
+
+        # There are no tags in the open tag counter.
+        assert all(v == 0 for v in list(obj.open_tag_counter.values()))
+
+        # The only tag in the tag stack is the one for the root
+        # document.
+        assert [obj.ROOT_TAG_NAME] == [x.name for x in obj.tagStack]
+
+    assertSoupEquals = assert_soup
+
+    def assertConnectedness(self, element: Tag) -> None:
+        """Ensure that next_element and previous_element are properly
+        set for all descendants of the given element.
+        """
+        earlier = None
+        for e in element.descendants:
+            if earlier:
+                assert e == earlier.next_element
+                assert earlier == e.previous_element
+            earlier = e
+
+    def linkage_validator(
+        self, el: Tag, _recursive_call: bool = False
+    ) -> Optional[PageElement]:
+        """Ensure proper linkage throughout the document."""
+        descendant = None
+        # Document element should have no previous element or previous sibling.
+        # It also shouldn't have a next sibling.
+        if el.parent is None:
+            assert (
+                el.previous_element is None
+            ), "Bad previous_element\nNODE: {}\nPREV: {}\nEXPECTED: {}".format(
+                el, el.previous_element, None
+            )
+            assert (
+                el.previous_sibling is None
+            ), "Bad previous_sibling\nNODE: {}\nPREV: {}\nEXPECTED: {}".format(
+                el, el.previous_sibling, None
+            )
+            assert (
+                el.next_sibling is None
+            ), "Bad next_sibling\nNODE: {}\nNEXT: {}\nEXPECTED: {}".format(
+                el, el.next_sibling, None
+            )
+
+        idx = 0
+        child = None
+        last_child = None
+        last_idx = len(el.contents) - 1
+        for child in el.contents:
+            descendant = None
+
+            # Parent should link next element to their first child
+            # That child should have no previous sibling
+            if idx == 0:
+                if el.parent is not None:
+                    assert (
+                        el.next_element is child
+                    ), "Bad next_element\nNODE: {}\nNEXT: {}\nEXPECTED: {}".format(
+                        el, el.next_element, child
+                    )
+                    assert (
+                        child.previous_element is el
+                    ), "Bad previous_element\nNODE: {}\nPREV: {}\nEXPECTED: {}".format(
+                        child, child.previous_element, el
+                    )
+                    assert (
+                        child.previous_sibling is None
+                    ), "Bad previous_sibling\nNODE: {}\nPREV {}\nEXPECTED: {}".format(
+                        child, child.previous_sibling, None
+                    )
+
+            # If not the first child, previous index should link as sibling to this index
+            # Previous element should match the last index or the last bubbled up descendant
+            else:
+                assert (
+                    child.previous_sibling is el.contents[idx - 1]
+                ), "Bad previous_sibling\nNODE: {}\nPREV {}\nEXPECTED {}".format(
+                    child, child.previous_sibling, el.contents[idx - 1]
+                )
+                assert (
+                    el.contents[idx - 1].next_sibling is child
+                ), "Bad next_sibling\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                    el.contents[idx - 1], el.contents[idx - 1].next_sibling, child
+                )
+
+                if last_child is not None:
+                    assert (
+                        child.previous_element is last_child
+                    ), "Bad previous_element\nNODE: {}\nPREV {}\nEXPECTED {}\nCONTENTS {}".format(
+                        child, child.previous_element, last_child, child.parent.contents
+                    )
+                    assert (
+                        last_child.next_element is child
+                    ), "Bad next_element\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                        last_child, last_child.next_element, child
+                    )
+
+            if isinstance(child, Tag) and child.contents:
+                descendant = self.linkage_validator(child, True)
+                assert descendant is not None
+                # A bubbled up descendant should have no next siblings
+                assert (
+                    descendant.next_sibling is None
+                ), "Bad next_sibling\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                    descendant, descendant.next_sibling, None
+                )
+
+            # Mark last child as either the bubbled up descendant or the current child
+            if descendant is not None:
+                last_child = descendant
+            else:
+                last_child = child
+
+            # If last child, there are non next siblings
+            if idx == last_idx:
+                assert (
+                    child.next_sibling is None
+                ), "Bad next_sibling\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                    child, child.next_sibling, None
+                )
+            idx += 1
+
+        child = descendant if descendant is not None else child
+        if child is None:
+            child = el
+
+        if not _recursive_call and child is not None:
+            target: Optional[Tag] = el
+            while True:
+                if target is None:
+                    assert (
+                        child.next_element is None
+                    ), "Bad next_element\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                        child, child.next_element, None
+                    )
+                    break
+                elif target.next_sibling is not None:
+                    assert (
+                        child.next_element is target.next_sibling
+                    ), "Bad next_element\nNODE: {}\nNEXT {}\nEXPECTED {}".format(
+                        child, child.next_element, target.next_sibling
+                    )
+                    break
+                target = target.parent
+
+            # We are done, so nothing to return
+            return None
+        else:
+            # Return the child to the recursive caller
+            return child
+
+    def assert_selects(self, tags: Iterable[Tag], should_match: Iterable[str]) -> None:
+        """Make sure that the given tags have the correct text.
+
+        This is used in tests that define a bunch of tags, each
+        containing a single string, and then select certain strings by
+        some mechanism.
+        """
+        assert [tag.string for tag in tags] == should_match
+
+    def assert_selects_ids(
+        self, tags: Iterable[Tag], should_match: Iterable[str]
+    ) -> None:
+        """Make sure that the given tags have the correct IDs.
+
+        This is used in tests that define a bunch of tags, each
+        containing a single string, and then select certain strings by
+        some mechanism.
+        """
+        assert [tag["id"] for tag in tags] == should_match
+
+
+class TreeBuilderSmokeTest(SoupTest):
+    # Tests that are common to HTML and XML tree builders.
+
+    @pytest.mark.parametrize(
+        "multi_valued_attributes", [None, {}, dict(b=["class"]), {"*": ["notclass"]}]
+    )
+    def test_attribute_not_multi_valued(self, multi_valued_attributes):
+        markup = '<html xmlns="http://www.w3.org/1999/xhtml"><a class="a b c"></html>'
+        soup = self.soup(markup, multi_valued_attributes=multi_valued_attributes)
+        assert soup.a["class"] == "a b c"
+
+    @pytest.mark.parametrize(
+        "multi_valued_attributes", [dict(a=["class"]), {"*": ["class"]}]
+    )
+    def test_attribute_multi_valued(self, multi_valued_attributes):
+        markup = '<a class="a b c">'
+        soup = self.soup(markup, multi_valued_attributes=multi_valued_attributes)
+        assert soup.a["class"] == ["a", "b", "c"]
+
+    def test_invalid_doctype(self):
+        # We don't have an official opinion on how these are parsed,
+        # but they shouldn't crash any of the parsers.
+        markup = "<![if word]>content<![endif]>"
+        self.soup(markup)
+        markup = "<!DOCTYPE html]ff>"
+        self.soup(markup)
+
+    def test_doctype_filtered(self):
+        markup = "<!DOCTYPE html>\n<html>\n</html>"
+        soup = self.soup(markup, parse_only=SoupStrainer(name="html"))
+        assert not any(isinstance(x, Doctype) for x in soup.descendants)
+
+    def test_custom_attribute_dict_class(self):
+        class MyAttributeDict(dict):
+            def __setitem__(self, key: str, value: Any):
+                # Ignore the provided value and substitute a
+                # hard-coded one.
+                super().__setitem__(key, "OVERRIDDEN")
+
+        markup = '<a attr1="val1" attr2="val2">f</a>'
+        builder = self.default_builder(attribute_dict_class=MyAttributeDict)
+        soup = self.soup(markup, builder=builder)
+        tag = soup.a
+        assert isinstance(tag.attrs, MyAttributeDict)
+        assert "OVERRIDDEN" == tag["attr1"]
+        tag["attr3"] = True
+        assert "OVERRIDDEN" == tag["attr3"]
+
+        expect = '<a attr1="OVERRIDDEN" attr2="OVERRIDDEN" attr3="OVERRIDDEN">f</a>'
+        assert expect == tag.decode()
+
+    def test_custom_attribute_value_list_class(self):
+        class MyCustomAttributeValueList(AttributeValueList):
+            def __init__(self, *args, **kwargs):
+                super().__init__(*args, **kwargs)
+                self.append("extra")
+
+        builder = self.default_builder(
+            multi_valued_attributes={"*": set(["attr2"])},
+            attribute_value_list_class=MyCustomAttributeValueList,
+        )
+        markup = '<a attr1="val1" attr2="val2">f</a>'
+        soup = self.soup(markup, builder=builder)
+        tag = soup.a
+        assert tag["attr1"] == "val1"
+        assert tag["attr2"] == ["val2", "extra"]
+        assert isinstance(tag["attr2"], MyCustomAttributeValueList)
+
+
+class HTMLTreeBuilderSmokeTest(TreeBuilderSmokeTest):
+    """A basic test of a treebuilder's competence.
+
+    Any HTML treebuilder, present or future, should be able to pass
+    these tests. With invalid markup, there's room for interpretation,
+    and different parsers can handle it differently. But with the
+    markup in these tests, there's not much room for interpretation.
+    """
+
+    def test_empty_element_tags(self):
+        """Verify that all HTML4 and HTML5 empty element (aka void element) tags
+        are handled correctly.
+        """
+        for name in [
+            "area",
+            "base",
+            "br",
+            "col",
+            "embed",
+            "hr",
+            "img",
+            "input",
+            "keygen",
+            "link",
+            "menuitem",
+            "meta",
+            "param",
+            "source",
+            "track",
+            "wbr",
+            "spacer",
+            "frame",
+        ]:
+            soup = self.soup("")
+            new_tag = soup.new_tag(name)
+            assert new_tag.is_empty_element is True
+
+        self.assert_soup("<br/><br/><br/>", "<br/><br/><br/>")
+        self.assert_soup("<br /><br /><br />", "<br/><br/><br/>")
+
+    def test_special_string_containers(self):
+        soup = self.soup("<style>Some CSS</style><script>Some Javascript</script>")
+        assert isinstance(soup.style.string, Stylesheet)
+        assert isinstance(soup.script.string, Script)
+
+        soup = self.soup("<style><!--Some CSS--></style>")
+        assert isinstance(soup.style.string, Stylesheet)
+        # The contents of the style tag resemble an HTML comment, but
+        # it's not treated as a comment.
+        assert soup.style.string == "<!--Some CSS-->"
+        assert isinstance(soup.style.string, Stylesheet)
+
+    def test_pickle_and_unpickle_identity(self):
+        # Pickling a tree, then unpickling it, yields a tree identical
+        # to the original.
+        tree = self.soup("<a><b>foo</a>")
+        dumped = pickle.dumps(tree, 2)
+        loaded = pickle.loads(dumped)
+        assert loaded.__class__ == BeautifulSoup
+        assert loaded.decode() == tree.decode()
+
+    def assertDoctypeHandled(self, doctype_fragment: str) -> None:
+        """Assert that a given doctype string is handled correctly."""
+        doctype_str, soup = self._document_with_doctype(doctype_fragment)
+
+        # Make sure a Doctype object was created.
+        doctype = soup.contents[0]
+        assert doctype.__class__ == Doctype
+        assert doctype == doctype_fragment
+        assert soup.encode("utf8")[: len(doctype_str)] == doctype_str
+
+        # Make sure that the doctype was correctly associated with the
+        # parse tree and that the rest of the document parsed.
+        assert soup.p is not None
+        assert soup.p.contents[0] == "foo"
+
+    def _document_with_doctype(
+        self, doctype_fragment: str, doctype_string: str = "DOCTYPE"
+    ) -> Tuple[bytes, BeautifulSoup]:
+        """Generate and parse a document with the given doctype."""
+        doctype = "<!%s %s>" % (doctype_string, doctype_fragment)
+        markup = doctype + "\n<p>foo</p>"
+        soup = self.soup(markup)
+        return doctype.encode("utf8"), soup
+
+    def test_normal_doctypes(self):
+        """Make sure normal, everyday HTML doctypes are handled correctly."""
+        self.assertDoctypeHandled("html")
+        self.assertDoctypeHandled(
+            'html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"'
+        )
+
+    def test_empty_doctype(self):
+        soup = self.soup("<!DOCTYPE>")
+        doctype = soup.contents[0]
+        assert "" == doctype.strip()
+
+    def test_mixed_case_doctype(self):
+        # A lowercase or mixed-case doctype becomes a Doctype.
+        for doctype_fragment in ("doctype", "DocType"):
+            doctype_str, soup = self._document_with_doctype("html", doctype_fragment)
+
+            # Make sure a Doctype object was created and that the DOCTYPE
+            # is uppercase.
+            doctype = soup.contents[0]
+            assert doctype.__class__ == Doctype
+            assert doctype == "html"
+            assert soup.encode("utf8")[: len(doctype_str)] == b"<!DOCTYPE html>"
+
+            # Make sure that the doctype was correctly associated with the
+            # parse tree and that the rest of the document parsed.
+            assert soup.p.contents[0] == "foo"
+
+    def test_public_doctype_with_url(self):
+        doctype = 'html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"'
+        self.assertDoctypeHandled(doctype)
+
+    def test_system_doctype(self):
+        self.assertDoctypeHandled('foo SYSTEM "http://www.example.com/"')
+
+    def test_namespaced_system_doctype(self):
+        # We can handle a namespaced doctype with a system ID.
+        self.assertDoctypeHandled('xsl:stylesheet SYSTEM "htmlent.dtd"')
+
+    def test_namespaced_public_doctype(self):
+        # Test a namespaced doctype with a public id.
+        self.assertDoctypeHandled('xsl:stylesheet PUBLIC "htmlent.dtd"')
+
+    def test_real_xhtml_document(self):
+        """A real XHTML document should come out more or less the same as it went in."""
+        markup = b"""<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hello.</title></head>
+<body>Goodbye.</body>
+</html>"""
+        with warnings.catch_warnings(record=True) as w:
+            soup = self.soup(markup)
+        assert soup.encode("utf-8").replace(b"\n", b"") == markup.replace(b"\n", b"")
+
+        # No warning was issued about parsing an XML document as HTML,
+        # because XHTML is both.
+        assert w == []
+
+    def test_namespaced_html(self):
+        # When a namespaced XML document is parsed as HTML it should
+        # be treated as HTML with weird tag names.
+        markup = b"""<ns1:foo>content</ns1:foo><ns1:foo/><ns2:foo/>"""
+        with warnings.catch_warnings(record=True) as w:
+            soup = self.soup(markup)
+
+        assert 2 == len(soup.find_all("ns1:foo"))
+
+        # n.b. no "you're parsing XML as HTML" warning was given
+        # because there was no XML declaration.
+        assert [] == w
+
+    def test_detect_xml_parsed_as_html(self):
+        # A warning is issued when parsing an XML document as HTML,
+        # but basic stuff should still work.
+        markup = b"""<?xml version="1.0" encoding="utf-8"?><tag>string</tag>"""
+        with warnings.catch_warnings(record=True) as w:
+            soup = self.soup(markup)
+            assert soup.tag.string == "string"
+        [warning] = w
+        assert isinstance(warning.message, XMLParsedAsHTMLWarning)
+        assert str(warning.message) == XMLParsedAsHTMLWarning.MESSAGE
+
+        # NOTE: the warning is not issued if the document appears to
+        # be XHTML (tested with test_real_xhtml_document in the
+        # superclass) or if there is no XML declaration (tested with
+        # test_namespaced_html in the superclass).
+
+    def test_processing_instruction(self):
+        # We test both Unicode and bytestring to verify that
+        # process_markup correctly sets processing_instruction_class
+        # even when the markup is already Unicode and there is no
+        # need to process anything.
+        markup = """<?PITarget PIContent?>"""
+        soup = self.soup(markup)
+        assert markup == soup.decode()
+
+        markup = b"""<?PITarget PIContent?>"""
+        soup = self.soup(markup)
+        assert markup == soup.encode("utf8")
+
+    def test_deepcopy(self):
+        """Make sure you can copy the tree builder.
+
+        This is important because the builder is part of a
+        BeautifulSoup object, and we want to be able to copy that.
+        """
+        copy.deepcopy(self.default_builder)
+
+    def test_p_tag_is_never_empty_element(self):
+        """A <p> tag is never designated as an empty-element tag.
+
+        Even if the markup shows it as an empty-element tag, it
+        shouldn't be presented that way.
+        """
+        soup = self.soup("<p/>")
+        assert not soup.p.is_empty_element
+        assert str(soup.p) == "<p></p>"
+
+    def test_unclosed_tags_get_closed(self):
+        """A tag that's not closed by the end of the document should be closed.
+
+        This applies to all tags except empty-element tags.
+        """
+        self.assert_soup("<p>", "<p></p>")
+        self.assert_soup("<b>", "<b></b>")
+
+        self.assert_soup("<br>", "<br/>")
+
+    def test_br_is_always_empty_element_tag(self):
+        """A <br> tag is designated as an empty-element tag.
+
+        Some parsers treat <br></br> as one <br/> tag, some parsers as
+        two tags, but it should always be an empty-element tag.
+        """
+        soup = self.soup("<br></br>")
+        assert soup.br.is_empty_element
+        assert str(soup.br) == "<br/>"
+
+    def test_nested_formatting_elements(self):
+        self.assert_soup("<em><em></em></em>")
+
+    def test_double_head(self):
+        html = """<!DOCTYPE html>
+<html>
+<head>
+<title>Ordinary HEAD element test</title>
+</head>
+<script type="text/javascript">
+alert("Help!");
+</script>
+<body>
+Hello, world!
+</body>
+</html>
+"""
+        soup = self.soup(html)
+        assert "text/javascript" == soup.find("script")["type"]
+
+    def test_comment(self):
+        # Comments are represented as Comment objects.
+        markup = "<p>foo<!--foobar-->baz</p>"
+        self.assert_soup(markup)
+
+        soup = self.soup(markup)
+        comment = soup.find(string="foobar")
+        assert comment.__class__ == Comment
+
+        # The comment is properly integrated into the tree.
+        foo = soup.find(string="foo")
+        assert comment == foo.next_element
+        baz = soup.find(string="baz")
+        assert comment == baz.previous_element
+
+    def test_preserved_whitespace_in_pre_and_textarea(self):
+        """Whitespace must be preserved in <pre> and <textarea> tags,
+        even if that would mean not prettifying the markup.
+        """
+        pre_markup = "<pre>a   z</pre>\n"
+        textarea_markup = "<textarea> woo\nwoo  </textarea>\n"
+        self.assert_soup(pre_markup)
+        self.assert_soup(textarea_markup)
+
+        soup = self.soup(pre_markup)
+        assert soup.pre.prettify() == pre_markup
+
+        soup = self.soup(textarea_markup)
+        assert soup.textarea.prettify() == textarea_markup
+
+        soup = self.soup("<textarea></textarea>")
+        assert soup.textarea.prettify() == "<textarea></textarea>\n"
+
+    def test_nested_inline_elements(self):
+        """Inline elements can be nested indefinitely."""
+        b_tag = "<b>Inside a B tag</b>"
+        self.assert_soup(b_tag)
+
+        nested_b_tag = "<p>A <i>nested <b>tag</b></i></p>"
+        self.assert_soup(nested_b_tag)
+
+        double_nested_b_tag = "<p>A <a>doubly <i>nested <b>tag</b></i></a></p>"
+        self.assert_soup(double_nested_b_tag)
+
+    def test_nested_block_level_elements(self):
+        """Block elements can be nested."""
+        soup = self.soup("<blockquote><p><b>Foo</b></p></blockquote>")
+        blockquote = soup.blockquote
+        assert blockquote.p.b.string == "Foo"
+        assert blockquote.b.string == "Foo"
+
+    def test_correctly_nested_tables(self):
+        """One table can go inside another one."""
+        markup = (
+            '<table id="1">'
+            "<tr>"
+            "<td>Here's another table:"
+            '<table id="2">'
+            "<tr><td>foo</td></tr>"
+            "</table></td>"
+        )
+
+        self.assert_soup(
+            markup,
+            '<table id="1"><tr><td>Here\'s another table:'
+            '<table id="2"><tr><td>foo</td></tr></table>'
+            "</td></tr></table>",
+        )
+
+        self.assert_soup(
+            "<table><thead><tr><td>Foo</td></tr></thead>"
+            "<tbody><tr><td>Bar</td></tr></tbody>"
+            "<tfoot><tr><td>Baz</td></tr></tfoot></table>"
+        )
+
+    def test_multivalued_attribute_with_whitespace(self):
+        # Whitespace separating the values of a multi-valued attribute
+        # should be ignored.
+
+        markup = '<div class=" foo bar	 "></a>'
+        soup = self.soup(markup)
+        assert ["foo", "bar"] == soup.div["class"]
+
+        # If you search by the literal name of the class it's like the whitespace
+        # wasn't there.
+        assert soup.div == soup.find("div", class_="foo bar")
+
+    def test_deeply_nested_multivalued_attribute(self):
+        # html5lib can set the attributes of the same tag many times
+        # as it rearranges the tree. This has caused problems with
+        # multivalued attributes.
+        markup = '<table><div><div class="css"></div></div></table>'
+        soup = self.soup(markup)
+        assert ["css"] == soup.div.div["class"]
+
+    def test_multivalued_attribute_on_html(self):
+        # html5lib uses a different API to set the attributes ot the
+        # <html> tag. This has caused problems with multivalued
+        # attributes.
+        markup = '<html class="a b"></html>'
+        soup = self.soup(markup)
+        assert ["a", "b"] == soup.html["class"]
+
+    def test_angle_brackets_in_attribute_values_are_escaped(self):
+        self.assert_soup('<a b="<a>"></a>', '<a b="&lt;a&gt;"></a>')
+
+    def test_strings_resembling_character_entity_references(self):
+        # "&T" and "&p" look like incomplete character entities, but they are
+        # not.
+        self.assert_soup(
+            "<p>&bull; AT&T is in the s&p 500</p>",
+            "<p>\u2022 AT&amp;T is in the s&amp;p 500</p>",
+        )
+
+    def test_apos_entity(self):
+        self.assert_soup(
+            "<p>Bob&apos;s Bar</p>",
+            "<p>Bob's Bar</p>",
+        )
+
+    def test_entities_in_foreign_document_encoding(self):
+        # &#147; and &#148; are invalid numeric entities referencing
+        # Windows-1252 characters. &#45; references a character common
+        # to Windows-1252 and Unicode, and &#9731; references a
+        # character only found in Unicode.
+        #
+        # All of these entities should be converted to Unicode
+        # characters.
+        markup = "<p>&#147;Hello&#148; &#45;&#9731;</p>"
+        soup = self.soup(markup)
+        assert "“Hello” -☃" == soup.p.string
+
+    def test_entities_in_attributes_converted_to_unicode(self):
+        expect = '<p id="pi\N{LATIN SMALL LETTER N WITH TILDE}ata"></p>'
+        self.assert_soup('<p id="pi&#241;ata"></p>', expect)
+        self.assert_soup('<p id="pi&#xf1;ata"></p>', expect)
+        self.assert_soup('<p id="pi&#Xf1;ata"></p>', expect)
+        self.assert_soup('<p id="pi&ntilde;ata"></p>', expect)
+
+    def test_entities_in_text_converted_to_unicode(self):
+        expect = "<p>pi\N{LATIN SMALL LETTER N WITH TILDE}ata</p>"
+        self.assert_soup("<p>pi&#241;ata</p>", expect)
+        self.assert_soup("<p>pi&#xf1;ata</p>", expect)
+        self.assert_soup("<p>pi&#Xf1;ata</p>", expect)
+        self.assert_soup("<p>pi&ntilde;ata</p>", expect)
+
+    def test_quot_entity_converted_to_quotation_mark(self):
+        self.assert_soup(
+            "<p>I said &quot;good day!&quot;</p>", '<p>I said "good day!"</p>'
+        )
+
+    def test_out_of_range_entity(self):
+        expect = "\N{REPLACEMENT CHARACTER}"
+        self.assert_soup("&#10000000000000;", expect)
+        self.assert_soup("&#x10000000000000;", expect)
+        self.assert_soup("&#1000000000;", expect)
+
+    def test_multipart_strings(self):
+        "Mostly to prevent a recurrence of a bug in the html5lib treebuilder."
+        soup = self.soup("<html><h2>\nfoo</h2><p></p></html>")
+        assert "p" == soup.h2.string.next_element.name
+        assert "p" == soup.p.name
+        self.assertConnectedness(soup)
+
+    def test_invalid_html_entity(self):
+        # The html.parser treebuilder can't distinguish between an
+        # invalid HTML entity with a semicolon and an invalid HTML
+        # entity with no semicolon (see its subclass for the tested
+        # behavior). But the other treebuilders can.
+        markup = "<p>a &nosuchentity b</p>"
+        soup = self.soup(markup)
+        assert "<p>a &amp;nosuchentity b</p>" == soup.p.decode()
+
+        markup = "<p>a &nosuchentity; b</p>"
+        soup = self.soup(markup)
+        assert "<p>a &amp;nosuchentity; b</p>" == soup.p.decode()
+
+    def test_head_tag_between_head_and_body(self):
+        "Prevent recurrence of a bug in the html5lib treebuilder."
+        content = """<html><head></head>
+  <link></link>
+  <body>foo</body>
+</html>
+"""
+        soup = self.soup(content)
+        assert soup.html.body is not None
+        self.assertConnectedness(soup)
+
+    def test_multiple_copies_of_a_tag(self):
+        "Prevent recurrence of a bug in the html5lib treebuilder."
+        content = """<!DOCTYPE html>
+<html>
+ <body>
+   <article id="a" >
+   <div><a href="1"></div>
+   <footer>
+     <a href="2"></a>
+   </footer>
+  </article>
+  </body>
+</html>
+"""
+        soup = self.soup(content)
+        self.assertConnectedness(soup.article)
+
+    def test_basic_namespaces(self):
+        """Parsers don't need to *understand* namespaces, but at the
+        very least they should not choke on namespaces or lose
+        data."""
+
+        markup = b'<html xmlns="http://www.w3.org/1999/xhtml" xmlns:mathml="http://www.w3.org/1998/Math/MathML" xmlns:svg="http://www.w3.org/2000/svg"><head></head><body><mathml:msqrt>4</mathml:msqrt><b svg:fill="red"></b></body></html>'
+        soup = self.soup(markup)
+        assert markup == soup.encode()
+        assert "http://www.w3.org/1999/xhtml" == soup.html["xmlns"]
+        assert "http://www.w3.org/1998/Math/MathML" == soup.html["xmlns:mathml"]
+        assert "http://www.w3.org/2000/svg" == soup.html["xmlns:svg"]
+
+    def test_multivalued_attribute_value_becomes_list(self):
+        markup = b'<a class="foo bar">'
+        soup = self.soup(markup)
+        assert ["foo", "bar"] == soup.a["class"]
+
+    #
+    # Generally speaking, tests below this point are more tests of
+    # Beautiful Soup than tests of the tree builders. But parsers are
+    # weird, so we run these tests separately for every tree builder
+    # to detect any differences between them.
+    #
+
+    def test_can_parse_unicode_document(self):
+        # A seemingly innocuous document... but it's in Unicode! And
+        # it contains characters that can't be represented in the
+        # encoding found in the  declaration! The horror!
+        markup = '<html><head><meta encoding="euc-jp"></head><body>Sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!</body>'
+        soup = self.soup(markup)
+        assert "Sacr\xe9 bleu!" == soup.body.string
+
+    def test_soupstrainer(self):
+        """Parsers should be able to work with SoupStrainers."""
+        strainer = SoupStrainer("b")
+        soup = self.soup("A <b>bold</b> <meta/> <i>statement</i>", parse_only=strainer)
+        assert soup.decode() == "<b>bold</b>"
+
+    def test_single_quote_attribute_values_become_double_quotes(self):
+        self.assert_soup("<foo attr='bar'></foo>", '<foo attr="bar"></foo>')
+
+    def test_attribute_values_with_nested_quotes_are_left_alone(self):
+        text = """<foo attr='bar "brawls" happen'>a</foo>"""
+        self.assert_soup(text)
+
+    def test_attribute_values_with_double_nested_quotes_get_quoted(self):
+        text = """<foo attr='bar "brawls" happen'>a</foo>"""
+        soup = self.soup(text)
+        soup.foo["attr"] = 'Brawls happen at "Bob\'s Bar"'
+        self.assert_soup(
+            soup.foo.decode(),
+            """<foo attr="Brawls happen at &quot;Bob\'s Bar&quot;">a</foo>""",
+        )
+
+    def test_ampersand_in_attribute_value_gets_escaped(self):
+        self.assert_soup(
+            '<this is="really messed up & stuff"></this>',
+            '<this is="really messed up &amp; stuff"></this>',
+        )
+
+        self.assert_soup(
+            '<a href="http://example.org?a=1&b=2;3">foo</a>',
+            '<a href="http://example.org?a=1&amp;b=2;3">foo</a>',
+        )
+
+    def test_escaped_ampersand_in_attribute_value_is_left_alone(self):
+        self.assert_soup('<a href="http://example.org?a=1&amp;b=2;3"></a>')
+
+    def test_entities_in_strings_converted_during_parsing(self):
+        # Both XML and HTML entities are converted to Unicode characters
+        # during parsing.
+        text = "<p>&lt;&lt;sacr&eacute;&#32;bleu!&gt;&gt;</p>"
+        expected = (
+            "<p>&lt;&lt;sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!&gt;&gt;</p>"
+        )
+        self.assert_soup(text, expected)
+
+    def test_smart_quotes_converted_on_the_way_in(self):
+        # Microsoft smart quotes are converted to Unicode characters during
+        # parsing.
+        quote = b"<p>\x91Foo\x92</p>"
+        soup = self.soup(quote, from_encoding="windows-1252")
+        assert (
+            soup.p.string
+            == "\N{LEFT SINGLE QUOTATION MARK}Foo\N{RIGHT SINGLE QUOTATION MARK}"
+        )
+
+    def test_non_breaking_spaces_converted_on_the_way_in(self):
+        soup = self.soup("<a>&nbsp;&nbsp;</a>")
+        assert soup.a.string == "\N{NO-BREAK SPACE}" * 2
+
+    def test_entities_converted_on_the_way_out(self):
+        text = "<p>&lt;&lt;sacr&eacute;&#32;bleu!&gt;&gt;</p>"
+        expected = "<p>&lt;&lt;sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!&gt;&gt;</p>".encode(
+            "utf-8"
+        )
+        soup = self.soup(text)
+        assert soup.p.encode("utf-8") == expected
+
+    def test_real_iso_8859_document(self):
+        # Smoke test of interrelated functionality, using an
+        # easy-to-understand document.
+
+        # Here it is in Unicode. Note that it claims to be in ISO-8859-1.
+        unicode_html = '<html><head><meta content="text/html; charset=ISO-8859-1" http-equiv="Content-type"/></head><body><p>Sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!</p></body></html>'
+
+        # That's because we're going to encode it into ISO-8859-1,
+        # and use that to test.
+        iso_latin_html = unicode_html.encode("iso-8859-1")
+
+        # Parse the ISO-8859-1 HTML.
+        soup = self.soup(iso_latin_html)
+
+        # Encode it to UTF-8.
+        result = soup.encode("utf-8")
+
+        # What do we expect the result to look like? Well, it would
+        # look like unicode_html, except that the META tag would say
+        # UTF-8 instead of ISO-8859-1.
+        expected = unicode_html.replace("ISO-8859-1", "utf-8")
+
+        # And, of course, it would be in UTF-8, not Unicode.
+        expected = expected.encode("utf-8")
+
+        # Ta-da!
+        assert result == expected
+
+    def test_real_shift_jis_document(self):
+        # Smoke test to make sure the parser can handle a document in
+        # Shift-JIS encoding, without choking.
+        shift_jis_html = (
+            b"<html><head></head><body><pre>"
+            b"\x82\xb1\x82\xea\x82\xcdShift-JIS\x82\xc5\x83R\x81[\x83f"
+            b"\x83B\x83\x93\x83O\x82\xb3\x82\xea\x82\xbd\x93\xfa\x96{\x8c"
+            b"\xea\x82\xcc\x83t\x83@\x83C\x83\x8b\x82\xc5\x82\xb7\x81B"
+            b"</pre></body></html>"
+        )
+        unicode_html = shift_jis_html.decode("shift-jis")
+        soup = self.soup(unicode_html)
+
+        # Make sure the parse tree is correctly encoded to various
+        # encodings.
+        assert soup.encode("utf-8") == unicode_html.encode("utf-8")
+        assert soup.encode("euc_jp") == unicode_html.encode("euc_jp")
+
+    def test_real_hebrew_document(self):
+        # A real-world test to make sure we can convert ISO-8859-9 (a
+        # Hebrew encoding) to UTF-8.
+        hebrew_document = b"<html><head><title>Hebrew (ISO 8859-8) in Visual Directionality</title></head><body><h1>Hebrew (ISO 8859-8) in Visual Directionality</h1>\xed\xe5\xec\xf9</body></html>"
+        soup = self.soup(hebrew_document, from_encoding="iso8859-8")
+        # Some tree builders call it iso8859-8, others call it iso-8859-9.
+        # That's not a difference we really care about.
+        assert soup.original_encoding in ("iso8859-8", "iso-8859-8")
+        assert soup.encode("utf-8") == (
+            hebrew_document.decode("iso8859-8").encode("utf-8")
+        )
+
+    def test_meta_tag_reflects_current_encoding(self):
+        # Here's the <meta> tag saying that a document is
+        # encoded in Shift-JIS.
+        meta_tag = (
+            '<meta content="text/html; charset=x-sjis" ' 'http-equiv="Content-type"/>'
+        )
+
+        # Here's a document incorporating that meta tag.
+        shift_jis_html = (
+            "<html><head>\n%s\n"
+            '<meta http-equiv="Content-language" content="ja"/>'
+            "</head><body>Shift-JIS markup goes here."
+        ) % meta_tag
+        soup = self.soup(shift_jis_html)
+
+        # Parse the document, and the charset is seemingly unaffected.
+        parsed_meta = soup.find("meta", {"http-equiv": "Content-type"})
+        content = parsed_meta["content"]
+        assert "text/html; charset=x-sjis" == content
+
+        # But that value is actually a ContentMetaAttributeValue object.
+        assert isinstance(content, ContentMetaAttributeValue)
+
+        # And it will take on a value that reflects its current
+        # encoding.
+        assert "text/html; charset=utf8" == content.substitute_encoding("utf8")
+
+        # No matter how the <meta> tag is encoded, its charset attribute
+        # will always be accurate.
+        assert b"charset=utf8" in parsed_meta.encode("utf8")
+        assert b"charset=shift-jis" in parsed_meta.encode("shift-jis")
+
+        # For the rest of the story, see TestSubstitutions in
+        # test_tree.py.
+
+    def test_html5_style_meta_tag_reflects_current_encoding(self):
+        # Here's the <meta> tag saying that a document is
+        # encoded in Shift-JIS.
+        meta_tag = '<meta id="encoding" charset="x-sjis" />'
+
+        # Here's a document incorporating that meta tag.
+        shift_jis_html = (
+            "<html><head>\n%s\n"
+            '<meta http-equiv="Content-language" content="ja"/>'
+            "</head><body>Shift-JIS markup goes here."
+        ) % meta_tag
+        soup = self.soup(shift_jis_html)
+
+        # Parse the document, and the charset is seemingly unaffected.
+        parsed_meta = soup.find("meta", id="encoding")
+        charset = parsed_meta["charset"]
+        assert "x-sjis" == charset
+
+        # But that value is actually a CharsetMetaAttributeValue object.
+        assert isinstance(charset, CharsetMetaAttributeValue)
+
+        # And it will take on a value that reflects its current
+        # encoding.
+        assert "utf8" == charset.substitute_encoding("utf8")
+
+        # No matter how the <meta> tag is encoded, its charset attribute
+        # will always be accurate.
+        assert b'charset="utf8"' in parsed_meta.encode("utf8")
+        assert b'charset="shift-jis"' in parsed_meta.encode("shift-jis")
+
+    def test_python_specific_encodings_not_used_in_charset(self):
+        # You can encode an HTML document using a Python-specific
+        # encoding, but that encoding won't be mentioned _inside_ the
+        # resulting document. Instead, the document will appear to
+        # have no encoding.
+        for markup in [
+            b'<meta charset="utf8"></head>' b'<meta id="encoding" charset="utf-8" />'
+        ]:
+            soup = self.soup(markup)
+            for encoding in PYTHON_SPECIFIC_ENCODINGS:
+                if encoding in (
+                    "idna",
+                    "mbcs",
+                    "oem",
+                    "undefined",
+                    "string_escape",
+                    "string-escape",
+                ):
+                    # For one reason or another, these will raise an
+                    # exception if we actually try to use them, so don't
+                    # bother.
+                    continue
+                encoded = soup.encode(encoding)
+                assert b'meta charset=""' in encoded
+                assert encoding.encode("ascii") not in encoded
+
+    def test_tag_with_no_attributes_can_have_attributes_added(self):
+        data = self.soup("<a>text</a>")
+        data.a["foo"] = "bar"
+        assert '<a foo="bar">text</a>' == data.a.decode()
+
+    def test_closing_tag_with_no_opening_tag(self):
+        # Without BeautifulSoup.open_tag_counter, the </span> tag will
+        # cause _popToTag to be called over and over again as we look
+        # for a <span> tag that wasn't there. The result is that 'text2'
+        # will show up outside the body of the document.
+        soup = self.soup("<body><div><p>text1</p></span>text2</div></body>")
+        assert "<body><div><p>text1</p>text2</div></body>" == soup.body.decode()
+
+    def test_worst_case(self):
+        """Test the worst case (currently) for linking issues."""
+
+        soup = self.soup(BAD_DOCUMENT)
+        self.linkage_validator(soup)
+
+
+class XMLTreeBuilderSmokeTest(TreeBuilderSmokeTest):
+    def test_pickle_and_unpickle_identity(self):
+        # Pickling a tree, then unpickling it, yields a tree identical
+        # to the original.
+        tree = self.soup("<a><b>foo</a>")
+        dumped = pickle.dumps(tree, 2)
+        loaded = pickle.loads(dumped)
+        assert loaded.__class__ == BeautifulSoup
+        assert loaded.decode() == tree.decode()
+
+    def test_docstring_generated(self):
+        soup = self.soup("<root/>")
+        assert soup.encode() == b'<?xml version="1.0" encoding="utf-8"?>\n<root/>'
+
+    def test_xml_declaration(self):
+        markup = b"""<?xml version="1.0" encoding="utf8"?>\n<foo/>"""
+        soup = self.soup(markup)
+        assert markup == soup.encode("utf8")
+
+    def test_python_specific_encodings_not_used_in_xml_declaration(self):
+        # You can encode an XML document using a Python-specific
+        # encoding, but that encoding won't be mentioned _inside_ the
+        # resulting document.
+        markup = b"""<?xml version="1.0"?>\n<foo/>"""
+        soup = self.soup(markup)
+        for encoding in PYTHON_SPECIFIC_ENCODINGS:
+            if encoding in (
+                "idna",
+                "mbcs",
+                "oem",
+                "undefined",
+                "string_escape",
+                "string-escape",
+            ):
+                # For one reason or another, these will raise an
+                # exception if we actually try to use them, so don't
+                # bother.
+                continue
+            encoded = soup.encode(encoding)
+            assert b'<?xml version="1.0"?>' in encoded
+            assert encoding.encode("ascii") not in encoded
+
+    def test_processing_instruction(self):
+        markup = b"""<?xml version="1.0" encoding="utf8"?>\n<?PITarget PIContent?>"""
+        soup = self.soup(markup)
+        assert markup == soup.encode("utf8")
+
+    def test_real_xhtml_document(self):
+        """A real XHTML document should come out *exactly* the same as it went in."""
+        markup = b"""<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN">
+<html xmlns="http://www.w3.org/1999/xhtml">
+<head><title>Hello.</title></head>
+<body>Goodbye.</body>
+</html>"""
+        soup = self.soup(markup)
+        assert soup.encode("utf-8") == markup
+
+    def test_nested_namespaces(self):
+        doc = b"""<?xml version="1.0" encoding="utf-8"?>
+<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
+<parent xmlns="http://ns1/">
+<child xmlns="http://ns2/" xmlns:ns3="http://ns3/">
+<grandchild ns3:attr="value" xmlns="http://ns4/"/>
+</child>
+</parent>"""
+        soup = self.soup(doc)
+        assert doc == soup.encode()
+
+    def test_formatter_processes_script_tag_for_xml_documents(self):
+        doc = """
+  <script type="text/javascript">
+  </script>
+"""
+        soup = BeautifulSoup(doc, "lxml-xml")
+        # lxml would have stripped this while parsing, but we can add
+        # it later.
+        soup.script.string = 'console.log("< < hey > > ");'
+        encoded = soup.encode()
+        assert b"&lt; &lt; hey &gt; &gt;" in encoded
+
+    def test_can_parse_unicode_document(self):
+        markup = '<?xml version="1.0" encoding="euc-jp"><root>Sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!</root>'
+        soup = self.soup(markup)
+        assert "Sacr\xe9 bleu!" == soup.root.string
+
+    def test_can_parse_unicode_document_begining_with_bom(self):
+        markup = '\N{BYTE ORDER MARK}<?xml version="1.0" encoding="euc-jp"><root>Sacr\N{LATIN SMALL LETTER E WITH ACUTE} bleu!</root>'
+        soup = self.soup(markup)
+        assert "Sacr\xe9 bleu!" == soup.root.string
+
+    def test_popping_namespaced_tag(self):
+        markup = '<rss xmlns:dc="foo"><dc:creator>b</dc:creator><dc:date>2012-07-02T20:33:42Z</dc:date><dc:rights>c</dc:rights><image>d</image></rss>'
+        soup = self.soup(markup)
+        assert str(soup.rss) == markup
+
+    def test_docstring_includes_correct_encoding(self):
+        soup = self.soup("<root/>")
+        assert (
+            soup.encode("latin1") == b'<?xml version="1.0" encoding="latin1"?>\n<root/>'
+        )
+
+    def test_large_xml_document(self):
+        """A large XML document should come out the same as it went in."""
+        markup = (
+            b'<?xml version="1.0" encoding="utf-8"?>\n<root>'
+            + b"0" * (2**12)
+            + b"</root>"
+        )
+        soup = self.soup(markup)
+        assert soup.encode("utf-8") == markup
+
+    def test_tags_are_empty_element_if_and_only_if_they_are_empty(self):
+        self.assert_soup("<p>", "<p/>")
+        self.assert_soup("<p>foo</p>")
+
+    def test_namespaces_are_preserved(self):
+        markup = '<root xmlns:a="http://example.com/" xmlns:b="http://example.net/"><a:foo>This tag is in the a namespace</a:foo><b:foo>This tag is in the b namespace</b:foo></root>'
+        soup = self.soup(markup)
+        root = soup.root
+        assert "http://example.com/" == root["xmlns:a"]
+        assert "http://example.net/" == root["xmlns:b"]
+
+    def test_closing_namespaced_tag(self):
+        markup = '<p xmlns:dc="http://purl.org/dc/elements/1.1/"><dc:date>20010504</dc:date></p>'
+        soup = self.soup(markup)
+        assert str(soup.p) == markup
+
+    def test_namespaced_attributes(self):
+        markup = '<foo xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"><bar xsi:schemaLocation="http://www.example.com"/></foo>'
+        soup = self.soup(markup)
+        assert str(soup.foo) == markup
+
+    def test_namespaced_attributes_xml_namespace(self):
+        markup = '<foo xml:lang="fr">bar</foo>'
+        soup = self.soup(markup)
+        assert str(soup.foo) == markup
+
+    def test_find_by_prefixed_name(self):
+        doc = """<?xml version="1.0" encoding="utf-8"?>
+<Document xmlns="http://example.com/ns0"
+    xmlns:ns1="http://example.com/ns1"
+    xmlns:ns2="http://example.com/ns2">
+    <ns1:tag>foo</ns1:tag>
+    <ns1:tag>bar</ns1:tag>
+    <ns2:tag key="value">baz</ns2:tag>
+</Document>
+"""
+        soup = self.soup(doc)
+
+        # There are three <tag> tags.
+        assert 3 == len(soup.find_all("tag"))
+
+        # But two of them are ns1:tag and one of them is ns2:tag.
+        assert 2 == len(soup.find_all("ns1:tag"))
+        assert 1 == len(soup.find_all("ns2:tag"))
+
+        assert 1, len(soup.find_all("ns2:tag", key="value"))
+        assert 3, len(soup.find_all(["ns1:tag", "ns2:tag"]))
+
+    def test_copy_tag_preserves_namespace(self):
+        xml = """<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
+<w:document xmlns:w="http://example.com/ns0"/>"""
+
+        soup = self.soup(xml)
+        tag = soup.document
+        duplicate = copy.copy(tag)
+
+        # The two tags have the same namespace prefix.
+        assert tag.prefix == duplicate.prefix
+
+    def test_worst_case(self):
+        """Test the worst case (currently) for linking issues."""
+
+        soup = self.soup(BAD_DOCUMENT)
+        self.linkage_validator(soup)
+
+
+class HTML5TreeBuilderSmokeTest(HTMLTreeBuilderSmokeTest):
+    """Smoke test for a tree builder that supports HTML5."""
+
+    def test_real_xhtml_document(self):
+        # Since XHTML is not HTML5, HTML5 parsers are not tested to handle
+        # XHTML documents in any particular way.
+        pass
+
+    def test_html_tags_have_namespace(self):
+        markup = "<a>"
+        soup = self.soup(markup)
+        assert "http://www.w3.org/1999/xhtml" == soup.a.namespace
+
+    def test_svg_tags_have_namespace(self):
+        markup = "<svg><circle/></svg>"
+        soup = self.soup(markup)
+        namespace = "http://www.w3.org/2000/svg"
+        assert namespace == soup.svg.namespace
+        assert namespace == soup.circle.namespace
+
+    def test_mathml_tags_have_namespace(self):
+        markup = "<math><msqrt>5</msqrt></math>"
+        soup = self.soup(markup)
+        namespace = "http://www.w3.org/1998/Math/MathML"
+        assert namespace == soup.math.namespace
+        assert namespace == soup.msqrt.namespace
+
+    def test_xml_declaration_becomes_comment(self):
+        markup = '<?xml version="1.0" encoding="utf-8"?><html></html>'
+        soup = self.soup(markup)
+        assert isinstance(soup.contents[0], Comment)
+        assert soup.contents[0] == '?xml version="1.0" encoding="utf-8"?'
+        assert "html" == soup.contents[0].next_element.name