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

EN TR, Transparency Mode 22-43
When transparency mode is off, all source pixels are written to the
destination, obscuring any underlying images.
Figure 22-23Transparency Mode = OFF
The transparency mode is defaulted by the
?E Reset, IN, or DF
commands.
Note For more information on the transparency mode, see the discussion
of the “Source Transparency Mode” in Chapter 13, The PCL Print
Model.