In pict.sty
PicTex offers the following definitions ‘\def\beginpicture{\setbox\!picbox=\hbox\bgroup....} \def\endpicture{... \egroup....}’, and it allows nested pictures.
<..pictex.4ht..>
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
% pictex.4ht 2014-07-12-22:36 %
% Copyright (C) 1997--2009 Eitan M. Gurari %
<.TeX4ht copyright.>
\let\:beginpicture=\beginpicture
\let\:endpicture=\endpicture
\def\beginpicture{%
\ifx \EndPicture\:UnDef
\a:pictex \expandafter\Picture\c:pictex{}%
\def\endpicture{\:endpicture \EndPicture\b:pictex}%
\fi\:beginpicture \def\beginpicture{\let\endpicture=\:endpicture
\:beginpicture}}
\NewConfigure{pictex}{3}
\Hinput{pictex}
\endinput
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