Then why not use the standard attribute syntax with a custom namespace (for example `[[xr0::alloc(result)]]`)? Compilers ignore attributes they do not implement

Then why not use the standard attribute syntax with a custom namespace (for example `[[xr0::alloc(result)]]`)? Compilers ignore attributes they do not implement (They may issue a warning, but one can either turn off that warning, or use macros to conditionally include the attributes).