HP PCL 5 Reference Manual page 34

Use these three rules to combine and shorten printer commands:
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1-8 Introduction to HP PCL
The first two characters after "?" (the parameterized and group
character) must be the same in all of the commands to be
combined. In the example above, these are "
All alphabetic characters within the combined printer command
are lower-case, except the final letter which is always upper-case.
In the combined example above, "O" becomes "o". The final
character in the printer command must always be upper-case to
let the printer know that the command is complete.
The printer commands are performed in the order that they are
combined (from left to right). Be sure to combine commands in
the order that they are to be performed.
" and "l".
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