IS VALID determines if another object has a valid value and then returns either ‘TRUE’ or FALSE’.

For an object to be valid it must be able to be evaluated properly.

IS VALID does not check to see if the value of an object is correct, it only checks to see if a valid value exists, in general 'null' is a valid value.

For an object reference where IS VALID returns FALSE, the object value will be the (typically percent) delimited name of the object reference.