import html5libhtml5lib.parseFragment('<math><tr><td><mo><tr>',                       container="td")

Traceback (most recent call last):  File "foo.py", line 5, in <module>    treebuilder="dom")  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 36, in parseFragment    return p.parseFragment(doc, container=container, encoding=encoding)  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 253, in parseFragment    self._parse(stream, True, container=container, encoding=encoding)  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 94, in _parse    self.mainLoop()  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 199, in mainLoop    new_token = phase.processStartTag(new_token)  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 480, in processStartTag    return self.startTagHandler[token["name"]](token)  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 2175, in startTagTableOther    self.closeCell()  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 2161, in closeCell    self.endTagTableCell(impliedTagToken("td"))  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/html5parser.py", line 2197, in endTagTableCell    self.tree.clearActiveFormattingElements()  File "/Users/gsnedders/Documents/my-projects/html5lib/html5lib-python/html5lib/treebuilders/_base.py", line 228, in clearActiveFormattingElements    entry = self.activeFormattingElements.pop()IndexError: pop from empty list