As yet, there is no book “Programming in LaTeX3”, and even if such a thing existed there would be lots of gaps. So there is no comprehensive support.
However, there are some 'resources':
- The “introduction to LaTeX3 ideas” in the expl3
documentation gives a broad-brush overview of the concepts.
- Joseph Wright has written a short series of
[[https://www.texdev.net/index.php?s=programming+latex3|blog posts]], which may help.
- There is also a complete command reference in the
The documents are still subject to development; some of the broader
design issues are discussed on the LaTeX mailing list
latex-l — you may subscribe to that list by sending a
message by sending a message
''subscribe latex-l <//your name//>''
to <a href=“mailto:listserv@urz.Uni-Heidelberg.de”>listserv@urz.Uni-Heidelberg.de</a>
Source: LaTeX3 programming