Ok, here's how this works:
- http://www.math.harvard.edu/texman/ is the default guide for all sites that have MathJax enabled. It's pretty generic, and that's a good thing.
- Any site with MathJax enabled can request that a different guide be used for this purpose. Ideally, they'll write one specific to the needs of their community, but if they want to link to Mathematics' guide instead that's fine too - as long as they don't mind it being specific to Math's needs in some ways (and, obviously, controlled by folks with editing rights on Math's meta).
At this moment (Feb. 12, 2019), 6 sites (plus 5 meta sites) have custom MathJax help pages:
- Physics (same as Mathematics)
- Physics Meta (same as Mathematics)
- Engineering Meta (same as Engineering)
- Earth Science
- Earth Science Meta (same as Earth Science)
- Chemistry Meta (same as Chemistry)
- Crypto Meta (same as Crypto)
Any other site wishing to change theirs should post a feature request on their meta site (ideally after writing their own guide).
Note: as of 3/13/2019, this also affects the "learn more" link shown on /editing-help#latex