3.24.3 Accepted Parameters for IF[N]DEF Directive
Masm's IF[N]DEF directive accepts user-defined symbols and registers, but fails for instructions, directives and other reserved words. JWasm's IF[N}DEF implementation accepts those symbols as well. OTOH, JWasm is a bit more picky and will display a warning if more than one item is found behind the directive - Masm just takes the first and silently skips the rest.Also see Member Argument for IF[N]DEF and .ERR[N]DEF Directives.