HP 8921A Programmer's Manual page 73

Guidelines for Operation
Command Names
The following topics discuss rules and guidelines for controlling the Test Set
through HP-IB.
All command names of more than four characters have an alternate abbreviated
form using only upper case letters and, in some cases, a single numeral. The
commands are not case sensitive. Upper and lower case characters can be used for
all commands.
For example, to set the destination of AF Generator 1 to Audio Out, any of the
following command strings are valid:
AFGENERATOR1:DESTINATION 'AUDIO OUT'
or
afgenerator1:destination 'audio out'
or
afg1:dest 'audio out'
or
AFG1:DEST 'AUDIO OUT'
or
Afg1:Dest 'Audio oUT'
Chapter 3, HP-IB Command Guidelines
Guidelines for Operation
73