This attribute is a boolean value which
specifies a default equinox and reference frame to use when reading a
FrameSet from a
FitsChan with
a foreign (i.e. non-native) encoding. It is only used if the FITS header contains RA and DEC axes but
contains no information about the reference frame or equinox. If this is the case, then values of FK4
and B1950 are assumed if the DefB1950 attribute has a non-zero value and ICRS is assumed if
DefB1950 is zero. The default value for DefB1950 depends on the value of the
Encoding
attribute: for FITS-WCS encoding the default is zero, and for all other encodings it is one.