Lexmark T642 Technical Reference page 206

The literal names in Table 4-4 are supported as PostScript emulation compatible
operators.
Table 4-4: Literal Names Supported
Supported
Not Supported
Literal Names
Literal Name Compatible Literal Name
monarcenvelope 3.875x7.5envelope
com10envelope 4.125x9.5envelope
dlenvelope 110x220envelope
c5envelope 162x229envelope
b5envelope 176x250envelope
Note: Duplexing is not supported on any envelope size. If duplex printing is
requested and one of the envelope size operators is sent to the printer,
duplexing is suspended until a paper size is requested that is supported for
duplex printing.
4-10
PostScript
Printer Models
W840