HP PCL/PJL reference (PCL 5 Printer Language) - Technical Reference Manual Part I

1-8 Introduction to HP PCL EN
Use these three rules to combine and shorten printer commands:
1 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 “
&” and “l”.
2 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.
3 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.