Fix a few incorrect descriptions.

[SVN r86661]
Create header for syntax highlighting stuff.

[SVN r86662]
Track the order of source mode tags.

So if there are two clashing source mode tags, then the latter one can
be used.

[SVN r86663]
Stack tagged source modes.

For when one tagged element is inside another.

[SVN r86664]
Support source code tagging for lists.

[SVN r86665]
Support source code tagging for paragraphs.

[SVN r86666]
Support source code tagging for sections.

[SVN r86667]
Document the new source mode changes.

[SVN r86668]