I can imagine only what suggests Karl - define some command to made dangerous commands no-op inside a group. Some example is attached.

(file #203)

Because pdflatex can accept \vskip inside \textsf{}
we may consider following proposal:
1. configure textsf to initial a flag to indicate that we have entered a new group and clear the flag that a new par has been generated

2. using \everypar to add a hook for a new par has been generated

3. In the hook of \everypar check whether we should generate the end of last par

Rongsong

Do you have any reason to use \vskip inside of \textsf? what is going on here is that \vskip closes current paragraph and start a new one, but this causes invalid xml, as starting and closing tags are in different paragraphs.

only way to fix that is to reset configuration for `textsf with

\Preamble{xhtml}
\begin{document}
\Configure{textsf}{}{}
\EndPreamble

this will use only formatting added in dvi postprocessing, instead of semantic tags.

but the correct solution is IMHO to not use \vskip inside of \textsf and other similar commands.