The usage of these is inconsistent. People use CCM below 1250A (and FM below 1150A), even though they really shouldn't. CCM89 itself defines the function down to 1000A, based on nonsense below 1250A (sorry, "extrapolation"). People have used both CCM and FM in the short FUV because what else were they going to do? I could remove the warnings if people think they're overly pedantic, but I can't add ValueError's. At least I didn't add a warning for r_v=3.1 to say "Really? Your sightline _really_ is exactly at the Galactic mean?"  ;)