You got me there. I should have said, man pages are my go-to for POSIX commands.

For Git, I usually turn to online documentation (at https://git-scm.com/docs) or, more often than not, search for keywords and, yes, end up at StackOverflow.

That supports the root-parent comment's point, that there are "fundamental design issues of POSIX", if users new and experienced must resort to such channels. It also implies that "man" as the default documentation system is not sufficiently meeting our needs.