65.4 seminar.cls

<..seminar.4ht..>
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % seminar.4ht                           2014-07-12-22:36 %
 % Copyright (C) 1999--2009       Eitan M. Gurari         %
 <.TeX4ht copyright.>
 
 \let\seminar:Hinput=\Hinput
 \def\Hinput#1{%
    \seminar:Hinput{#1}%
    \def\:temp{#1}\def\:tempa{article}\ifx \:temp\:tempa
       \let\Hinput=\seminar:Hinput
       \input seminar-a.4ht
    \fi
 }
 \endinput
 -_-_-

The seminar class loads the article class, and then its own definitions.

<..seminar-a.4ht..>
 %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
 % seminar-a.4ht                         2014-07-12-22:36 %
 % Copyright (C) 1999--2009       Eitan M. Gurari         %
 <.TeX4ht copyright.>
 <.seminar code.>
 \Hinput{seminar}
 \endinput
 -_-_-

<..seminar code..>
 \def\begin@slide[#1,#2]{\begingroup
    \slide@clearpage   \slidetrue \leavevmode   \refstepcounter{slide}%
    \the\slide@hook   \the\before@newslide
    \everyslide}
 \def\end@slide{\endgroup}
 -_-_-