HP PCL 5 Reference Manual page 163

TrueType example: If a symbol set based on Unicode numbers
requires one or more characters from the standard ASCII collection
and some of the characters from the Latin 5 collection, then bits 31,
28 and 0 are set to one (refer to Appendix D in the PCL 5 Comparison
Guide for information regarding the various symbol collections).
As stated above, to determine which unbound scalable fonts contain
the symbols for the specific symbol set, the printer must identify those
unbound fonts that contain the symbol collections of the requested
symbol set. To do this, the printer accesses the Character
Requirements number for the requested symbol set. If, for example,
the Roman-8 symbol set was requested, the printer would access the
Character Requirements number from the Roman-8 symbol set
information in the printer. This number is then compared with the
Character Complement number of each unbound font in the printer. If
any matches are found, those unbound fonts are included in the list of
potential fonts for selection.
Final Font Selection
After the process above is complete, the printer contains a list of all
fonts (bitmap, bound, and unbound) which support the requested
symbol set. (If no fonts are found for the specified symbol set,
Roman-8 is used. If more than one font remains, the printer continues
comparing font selection characteristics, eliminating fonts, until only
one remains. Whenever only one font remains, it is selected for
printing.
Symbol Set Mapping Table
The printer receives character codes in the range 0-255 which,
depending on the selected symbol set, identify the symbols to print or
control codes to execute.
There are hundreds of symbols available in unbound fonts in
HP LaserJet printers, more than can be identified by the character
code range (0 - 255). A list of these symbols is provided in the
symbol indexes, such as the Master Symbol List (MSL) and the
Unicode list In Appendix D of the PCL 5 Comparison Guide). Each
symbol in the list is identified by a unique MSL or Unicode number.
Symbols in unbound fonts are identified by this number.
Unbound Scalable Fonts 9-11
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