Hi Jonathan,

On Wed, Sep 1, 2021 at 11:45 AM you wrote in part:

 I'd like to see an online LaTeX syntax checker, that's linked to a help system.

In 1998 I concluded that such a thing is impossible if it is to include all documents that run "correctly" -- hard to define, e.g. think about $f(x$) -- through latex the program (which now is one of pdflatex, xetex, or lualatex -- maybe also the various guises of tex4ht and latexml).

It is possible, however, if one restricts to documents under a LaTeX profile, as I explained at TUG 2010 in my talk "LaTeX Profiles as Objects in the Category of Markup Languages".

                 -- Bill

William F Hammond
Email: [log in to unmask]