[tex4ht] Detecting TeX4ht

[Karl Berry]

Hi Denis,

      \newif\ifhttex \ifx\HCode\undefined \httexfalse \else \httextrue \fi

Sorry for the late reply.  I just wanted to chime in that I also have
always used \ifx\HCode.

Although I understand and even agree with Eitan's response in principle
(to use configuration files), in practice it is just too much trouble.
And configuration files are barely documented at all, as far as I know.

Best,
karl