Ok, here's how this works:
- https://legacy-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.SE's 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).
As of April 21, 2023, 14 sites (and their corresponding meta sites) have customized MathJax help links:
Any other site wishing to change theirs should post a feature request on their meta site (ideally after writing their own guide). If the community agrees on what URL their MathJax help link should point to, the site's moderators can add the status-review tag to the meta post to escalate the request for staff attention.
Note: as of March 13, 2019, this setting also affects the "Learn more: MathJax help" link shown on