.MACRO begins the definition of a macro. It gives the macro name
    and a list of formal arguments. The .MACRO directive is followed
    by the source text to be included in the macro expansion. The
    .ENDM directive specifies the end of the range.

    Macro names do not conflict with user-defined symbols. Both a
    macro and a user-defined symbol can have the same name.

    When the assembler encounters a .MACRO directive, it adds the
    macro name to its macro name table and stores the source text
    of the macro (up to the matching .ENDM directive). No other
    processing occurs until the macro is expanded.

    The symbols in the formal argument list are associated with the
    macro name and are limited to the scope of the definition of that
    macro. For this reason, the symbols that appear in the formal
    argument list can also appear elsewhere in the program.