i don't think we can currently support this in jPDL 3. it would require big changes, including schema updates that will be forced to all our user base.
i do plan to make that separation in the next version of jPDL 4.
at the time, i thought it was a cool thing that you didn't have to separate between value binding expressions and method binding expressions.
now i still think that is cool, but the compatibility with what people know of unified expressions wins over the coolness argument.
Yeah, it doesn't actually do any damage to the evaluation of the expressions, just means we can't throw the exceptions that people are used to with Unified EL. I was half way through a set of if-then-else statements to allow us throw a generic exception and log the possible specific exceptions so I will finish that off as a workaround for now.