newbie here.. looking for fx_* documentation

Sorry I’m no, just looking for documentation on these awesome filters I see in the gallery.
like say fx_feltpen … and really just looking for a list of fx_ functions. I’ll even settle for looking through the source code.

stdlib is here:
contains all the source code

fx_feltpen is really simple actually:

fx_feltpen :
  foreach { +fx_hardsketchbw ${1-5},0,0 blend hardlight erode_oct $6 }