HP PCL 5 Reference Manual page 224

The optional cvt, fpgm and prep tables, as defined in True Type Font
Files, typically appear in the Global TrueType Data Segments of
hinted TrueType soft fonts, but should not appear in unhinted fonts.
IF (Intellifont Face Data) Reserved for future use.
PA (PANOSE Description) This data segment of variable length may
be used for the purpose of font selection and substitution. Its
definition continues to evolve. A 10-field (10-byte) version sufficient
for the description of most Latin fonts appears under the OS/2 table
in True Type Font Files.
PF (PS-Compatible Font Name) Reserved for future use.
XW (x-windows font name) This ASCII field contains standard
X-Windows font names.
Checksum
The value of this byte, when added to the sum of all of the bytes from
byte 64 of the descriptor through the Reserved byte, should equal 0 in
modulo 256 arithmetic.
11-42 Soft Font Creation
EN