Optional
Only groups of this IFC class or a subclass, e.g. IfcSystem. Absent = any IfcGroup.
IfcSystem
IfcGroup
Matched against each group's Name. Ignored for isSet / isNotSet.
isSet
isNotSet
How value reads. Only consulted by the matches / notMatches ops.
value
matches
notMatches
Only groups of this IFC class or a subclass, e.g.
IfcSystem. Absent = anyIfcGroup.