* If a phrase becomes italicized, it should show the non-italic version in red and immediately after, the italic
version in green.
This required doing a pass on the HTML to merge certain elements together before doing the actual diff.
strings. Not perfect yet. For instance, if string a contains "foo bar baz" and
string b contains "foo <i>bar</i> baz", the resulting output does not show
"bar" in strikeout and "<i>bar</i>" in green, as one might expect.