from: https://www.jmp.com/support/help/en/18.1/?os=win&source=application#page/jmp/advanced-expressions-ma...
If you assign the expression x+y to a, quoting it as an expression with Expr, then whenever a is evaluated, it evaluates the expression using the current values of x and y and returns the result.
Exceptions are the utilities Show, Write, and Print, which do not evaluate expressions for pure name arguments.
x=5;
y=10;
a=expr(x+y);
Show( a ); // x + y
Show(Name Expr(a)); // x + y
Show(x+y); // 15
Show(x,y); // 5, 10
I wonder if Show, Write and Print are the only exceptions ...
