Am Fri, 14 Jan 2022 08:44:06 +0100 schrieb Robert Alessi:

> Dear List,
> 
> Something happened with today's update.
> 
> Any of the -dev engines fail to compile the attached .dtx file if the
> “dox” package is loaded, but I am not sure the failure is caused by
> this package.
> 
> (pdf|xe|lua)latex-dev engines seem to bump into \@doc@describe which
> is defined in doc-v3beta.sty.

the new doc version used in latex-dev incorporates a few ideas of
dox, see the documentation. Beside others it now also defines the
command \SpecialMacroIndex, and defines it defined
\SpecialUsageIndex with it:

\def\SpecialUsageIndex{\SpecialMacroIndex}.

As dox then does \let\SpecialMacroIndex\SpecialUsageIndex
this loops.

Probably dox would need a fix here, it should check if
\SpecialMacroIndex is already defined. If I change dox to use

\@ifundefined{SpecialMacroIndex}{\let\SpecialMacroIndex\SpecialUsageIndex}{}

your skeleton compiles.

Thanks for trying latex-dev. It helps to identify such problems :-)

Ulrike