DMN11 — Expression defined as resulting in single value, but Decision may have multiple values

This is related to DMN11-9. Expression class is defined in 7.3 and 7.3.1 as "return a single value when interpreted", but Decision (e.g. DecisionTable, concrete subclass of Expression) may return multiple values, in two ways. Compound output tables, and multi-hit Collect tables. I suggest removing the "single value" comment from definition of Expression, or applying it only to a different class than the superclass of DecisionTable.

Revise text to clarify Expression as "single value".