我是这样理解的，不知道对不对？

%nrstr mask  &a 的resolve，所以b是&a，而不是begin

upcase(&b)就是 &A

但是qupcase resolve &&a为&a， 也就是a的值 begin

The %UPCASE and %QUPCASE functions convert lowercase characters in the argument to uppercase. %UPCASE does not mask special characters or mnemonic operators in its result, even when the argument was previously masked by a macro quoting function.

If the argument contains a special character or mnemonic operator, listed below, use %QUPCASE. %QUPCASE masks the following special characters and mnemonic operators in its result:

& % ' " ( ) + - * / < > = &not; ^ ~ ; , # blank
AND OR NOT EQ NE LE LT GE GT IN

%UPCASE and %QUPCASE are useful in the comparison of values because the macro facility does not automatically convert lowercase characters to uppercase before comparing values.