.ap
.rm 70
.lm 0
1 UNMESSAGE
.lm 1
.i+5;UNMESSAGE [message-file] (defaults to SYS$MESSAGE:SYSMSG.EXE)

 Decompiles message files. Note, the decompiled message file will
not be exactly the same as the original, as certain information 
is not stored in these files. However, the message text files
created can be rerun through the message compiler (MESSAGE) and
the resulting file will produce exactly the same results as the
original (I think).
.lm 0
/OUTPUT
.lm 1
.i+5;/OUTPUT=file-spec
.blank
 Specifies an output file to store the decompiled message text.