A symbol in the operator field can be either a permanent symbol
    or a macro name. MACRO-64 searches for a symbol definition in the
    following order:

    1. Macro and conditional directives:

       .ELSE      .ENDC          .ENDM
       .ENDR      .IF            .IF_FALSE (.IFF)
       .IF_TRUE   .IF_TRUE_      .IIF
       (.IFT)     FALSE (.IFTF)
       .INCLUDE   .IRP           .IRPC
       .LIBRARY   .MACRO         .MCALL
       .MDELETE   .MEXIT         .NARG
       .NCHAR     .REPEAT

    2. Previously defined macro names

    3. Permanent symbols (instructions and other directives)

    This search order allows most permanent symbols, except
    conditional directives and macro directives, to be redefined
    as macro names. If a symbol in the operator field is not defined
    as a macro or a permanent symbol, the assembler displays an error
    message.