currently there's a help file only for [expr], so if you ask for help on [expr~]/[fexpr~] you get only information on [expr].

Don't know if there are special help files for [expr~]/[fexpr~] and they're just not called, but in vanilla there's only one help file for the whole family, and it has been largely updated by me in Pd 0.48 and 0.48-1 to include all functionalities.

By the way, Pd 0.48-1 carries a newer version (expr 0.55) than 0.48-0 (expr 0.5).

Seems expr in Purr Data has been updated to 0.55 from 0.48-0, if no further updates are to happen, at least the help files should be upgraded/fixed.

cheers