- update to 4.2.1:
* The default XML formatter will now replace ampersands even if they
appear to be part of entities. That is, "<" will become
"&lt;". The old code was left over from Beautiful Soup 3, which
didn't always turn entities into Unicode characters.

If you really want the old behavior (maybe because you add new
strings to the tree, those strings include entities, and you want
the formatter to leave them alone on output), it can be found in
EntitySubstitution.substitute_xml_containing_entities(). [bug=1182183]

* Gave new_string() the ability to create subclasses of
NavigableString. [bug=1181986]

* Fixed another bug by which the html5lib tree builder could create a
disconnected tree. [bug=1182089]

* The .previous_element of a BeautifulSoup object is now always None,
not the last element to be parsed. [bug=1182089]

* Fixed test failures when lxml is not installed. [bug=1181589]

* html5lib now supports Python 3. Fixed some Python 2-specific
code in the html5lib test suite. [bug=1181624]

* The html.parser treebuilder can now handle numeric attributes in
text when the hexidecimal name of the attribute starts with a
capital X. Patch by Tim Shirley. [bug=1186242]