This printer language command is used at the beginning and end of every printer data stream. Usually it is already in the data stream, especially printing via Windows or SAP.
It is used to separate data streams. It is for example definitively needed for the stapling commands.

Syntax: <ESC>%-12345X

So every PCL5 print job should begin with:

<ESC>%-12345X@PJL
@PJL ....
@PJL...
....
@PJL ENTER LANGUAGE=PCL

and ends with:

<ESC>%-12345X

<ESC> is representing the Escape sign: ASCII 27 or hex 1B

If this is not the case, it is strongly recommended to use the ELP_Command=ET; This wraps the job into UEL statements and provides a well formed PJL header.

Tip: Install notepad++ on your PC/server to have a great editor for looking at ELP configuration files and data streams.

ELP_Commands     @PCL Commands    PJL Commands