[fitsbits] Any bad pixel mask convention?

[Richard J. Mathar]

Is there something like a bad pixel mask FITS standard that stores bad pixels
with a boolen value or perhaps a float where 1=good, NaN=bad in FITS images?
Should one use a BLANK value combined with a byte or integer image or is
it best to invent a private ASCII format for this purpose?

R. J. Mathar