With mnemonic tagging, you can add a ":ASM" or ":MAC" suffix to an operation code. The mnemonic directs the assembler in this way:

:ASM

The assembler searches for machine or assembler instructions only. Macros of the same name are ignored. If the operation code is not found, then the search ends.

:MAC

The assembler searches for macro instructions only. Machine and assembler instructions are ignored. If the entry is not found in the current table, then a search for a definition of opcode is done on SYSLIB (the normal search).

For example, say there is a machine code entry named AR. Then AR finds that entry (no change). AR:ASM is the same; the assembler looks for a machine or assembler instruction. With AR:MAC, the assembler looks for a macro named AR. If it is not found in the internal table then the assembler searches on SYSLIB. Assuming AR is found, the assembler adds a macro entry for AR to the table, and this entry is used for this instruction.