The following beamer document uses handout mode to generate two frames.
\documentclass[handout]{beamer}
\usepackage{xparse}
\NewDocumentEnvironment{frm}{+b}
\ExplSyntaxOn
{%
\makeatletter
\gdef\beamer@currentmode{beamer}
\makeatother%
\begin{frame}
#1
\end{frame}
\makeatletter
\gdef\beamer@currentmode{handout}
\makeatother%
}{}
\ExplSyntaxOff
\begin{document}
\begin{frm}
hello \pause world
\end{frm}
\makeatletter
\gdef\beamer@currentmode{beamer}
\makeatother%
\begin{frame}
hello \pause world
\end{frame}
\makeatletter
\gdef\beamer@currentmode{handout}
\makeatother%
\end{document}
The second frame is wrapped in code meant to temporarily switch from handout to beamer mode. The first frame should be identical to the second, but something is going wrong with this custom environment (the animation shows up in the second frame but not the first).
What is going wrong here?
