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

EN Set Compression Method Command 15-21
If more than eight replacement (delta) bytes are needed, additional
command byte/replacement bytes may be added, as shown below:
E
C
*3m#W [(Command Byte)(1 to 8 Replacement
Bytes)][(Command Byte)(1 to 8 Replacement Bytes)]. . .
In the command byte, the upper three bits identify the number of
replacement (delta) bytes (which can be 1 to 8 bytes). The lower five
bits identify the location the replacement bytes are to be positioned.
This position is identified as some number of bytes in, from the first
untreated byte, referred to as the offset. For example, if there are 5
replacement bytes and the offset is 7, then the replacement bytes
replace byte 7, 8, 9, 10, and 11 (the five bytes beginning at byte 7
from the seed row).
If there is more than one replacement in a row, the second offset is
counted from the next untreated byte in the row: the first byte
following the last replacement byte.
Figure 15-9
Table 15-7
Command Byte
7540
Number of bytes to replace (1-8) Relative offset from last
untreated byte