Description%expand expands its argument as a macro. This is VERY unsafe to do with user-supplied content, please use safe-expand instead.
Typical usage for %expand is to partition code into libraries and then load them as needed, for example %expand(%include(/path/to/file)) will evaluate the contents of that file, potentially creating or redefining functions.
%set(x,%%iadd(1,1)) The result of %x% is %expand(%x%). ----- The result of %iadd(1,1) is 2.
See Alsosafe-expand | invoke