HP PCL/PJL reference - Printer Job Language Technical Reference Manual

4-8 Kernel Commands EN
particular printer language. Once it recognizes the printer
language, the printer backs up to the beginning of the sampled
print data and switches to the printer language determined to
be most appropriate. Then it begins to parse the data in the
newly selected printer language.
Note HP LaserJet 4V and 4MV printers cannot properly context-switch into
the ESC/P personality by sensing the data stream. Developers who
use ESC/P must use explicit or implicit switching.
Although printers supporting context switching can select printer
languages accurately, we recommend that every job containing
printable data include an ENTER LANGUAGE command to explicitly
select the correct printer language. This method improves
performance and eliminates unintentional printer language switching,
which can potentially cause data loss. Performance is not adversely
affected if both the application and the spooler send the ENTER
LANGUAGE command.
Figure 4-1 Switching Printer Languages