Interpretation of PROHIBITED for property requirement :ballot_box:

**Problem:**

PROHIBITED seems to be interpreted as negation, but is missleading from an engineering point of view due to the mandatory datatype settings.

Current interpretation of PROHIBITED:
`NOT EXISTS (Pset=="My_Pset" AND Property=="My_Property" AND IfcMeasure=="IFCLABEL")
`
My expectation as engineer would however be more like this: (if I would like to exclude a property I do not care about the datatype)
`NOT EXISTS (Pset=="My_Pset" AND Property=="My_Property")`

**Proposed solution:**

- make datatype optional (or ignore in PROHIBITED requirements)
- add logical statements to documentation for interpretation of PROHIBITED, REQUIRED and OPTIONAL
(for OPTIONAL: IF Pset AND Property THEN Datatype AND Value)

P.S.:
REQUIRED (minOccurs=1) is clear, although I would expect maxOccurs=1 instead of unbounded because the required property should be present once, but not more than once, and asking for a number of properties with a pattern does not make sense to me.