This object along with xcmPrtInterpPCLPtSizeDenominatr sets the
default for the PCL-specific PJL variable 'PTSIZE'.
The PTSIZE variable only applies when the FONTNUMBER setting
specifies a scalable proportionally-spaced font.
The size is in units of printer's points, which units are here
considered to be exactly 1/72 of an inch.
The value zero shall mean not specified.