HP 4 FAMILY - Manual (Page 117)

Operation Description
21 Deletes the macro association named by the current Macro ID. The
macro must have been associated with an alphanumeric Macro ID (using
operation 4). No String ID is supplied (?&n1W21). This command removes
the alphanumeric macro name association, however the disk resource itself is
not changed.
100 Media select (see media selection table). Media types are specified using
the printer control panel. The following table indicates which media type and
paper size is used in the various media-select situations.
Note PCL objects stored on the printer disk cannot be deleted,
set to temporary, set to permanent, or modified in any way
using the PCL language.
Printer-Specific Differences 2-81