 must leave all whitespace characters intact (with the exception of
leading and trailing whitespace characters, which should be removed).
Otherwise, whitespace
is handled according to the following rules:
</p>

<ul>
<li>
All whitespace surrounding block elements should be removed.
</li>
<li>
Comments are removed entirely and do not affect whitespace handling. One
whitespace character on either side of a comment is treated as two white
space characters.
</li>
<li>
Leading and trailing whitespace inside a blo