https://davidcarlisle.github.io/uk-tex-faq/
https://ctan.org/tex-archive/info/knuth-pdf
https://www.ctan.org/pkg/texinfo
https://davidcarlisle.github.io/uk-tex-faq/FAQ-LaTeX2HTML.html
https://www.w3.org/Tools/Word_proc_filters.html
https://davidcarlisle.github.io/uk-tex-faq/FAQ-mathml.html
--
https://ctan.org/pkg/l3kernel
https://stackoverflow.com/questions/2918449/inlining-the-latex-input-command
https://ctan.org/tex-archive/support/flatten
https://ctan.org/tex-archive/support/flatex
http://www.math.tau.ac.il/~sariel/flatex.html
https://mirror.funkfreundelandshut.de/latex/macros/latex/required/l3kernel/expl3.pdf
https://tex.stackexchange.com/questions/24932/moving-to-latex3-for-package-authors
https://ctan.org/pkg/l3packages