[tex4ht] [bug #477] Support for new LaTeX hook management

[Ulrike Fischer]

>> while there certainly can/will be problems, this error here seems to be
>> unrelated to \DocumentMetadata. I get an error with make4ht also for this:
>>

> thanks for this example. You are right. It seems that packages added
> in \AddToHook{begindocument/before} or \AtBeginDocument are ignored
> too. It is strange because I thought .4ht files captured them, but
> they are not.

> I was able to fix these hooks issues by manually calling:

> \ifdefined\UseHook
> \UseHook {begindocument/before}
> \UseHook {begindocument}
> \RemoveFromHook{begindocument/before}
> \RemoveFromHook{begindocument}
> \fi

This won't fix the error with \DocumentMetadata as the 
testphase code loads there amsmath not with the standard hooks but in 
our own hook:

\tl_gput_right:Nn \@kernel at before@begindocument
  { \RequirePackage { amsmath } }
  
(which doesn't look right, but moving it to 
\@kernel at after@begindocument at before doesn't work either). 

We could probably load amsmath earlier, but naturally the problem 
could reappear with other packages or code.

> in redefinition of the \document command in tex4ht.sty. I wonder if it
> wouldn't break something else, as in the original version of
> \document, the begindocument hook is called much later, after setting
> various variables. It can break some things in theory. However, the
> variables are mainly related to line width and similar stuff, which
> don't matter much in the conversion process.


Well I know that rewriting such patches is hard, but this \document
redefinition looks very fragile. Sadly I can't make a concrete suggestion
how to change it as I have no idea what all the code is doing and what
should come before and after other things.

Ulrike