FX files - no SDK info when seem to be required

There is no information about fx files, yet the lightdef description requires
a fx file be referenced. FX files seem to be from legacy FSX, but are not
depricated or no path has been stipulated for VFX migration. Could you add
back in the missing FSX information about fx files, perhaps the FX editor too.
Or please describe the new way to make light effects. Can I just not find the
SDK info on fx files?