`\ifhtlatex` needed for running tex4ht with different code [duplicate]

Question

It is much easier to write my texts in an editor with LaTeX, but often clients ask for a word file.

tex4ht does a good job, it produces html from a tex-file, which can be easily used. But there are some packages which cause errors, e.g. the §-sign of Linux Libertine. Is it possible to have a command which makes pdflatex have a look whether it is run by htlatex?

I'd like to write something like

 \ifhtlatex
\usepackage{lmodern}
\else 
\usepackage{libertine}
\fi

There are more things that don't work with htlatex, e.g. the machinery to name and count exhibitions and to produce a list of them at documents end. So something like \ifhtlatex would be helpfull.

==========

I dont't want to load the tex4ht package itself, so I've no idea, how this question could be helpfull...

Answer 1

htlatex loads package tex4ht via the hook \@documentclasshook that is called at the end of the document class. Thus you can test for this package after \documentclass:

\documentclass[...]{...}
\makeatletter
\newif\ifhtlatex
\@ifpackageloaded{tex4ht}{\htlatextrue}{\htlatexfalse}
\makeatother

Before \documentclass the macro \HCode could be checked that is defined by htlatex, e.g.:

\newif\ifhtlatex
\ifx\HCode\UnDeFiNeD
  \htlatexfalse
\else
  \htlatextrue
\fi
\documentclass{...}