Currently, contexts must be expressed in "naked" form:
but it's often convenient to express the context through a variable, which is exactly what the ifvarclass attribute does.
It would be terrific if the parser allowed strings with variables in the context expressions as well; as far as the language goes, this is not new functionality but simply syntactic sugar.
If a user specifies both a string context and an ifvarclass attribute, the outcome should simply be the AND of the two conditions. So there's no ambiguity and this change is fully backwards compatible with all current CFE code.