I have answered this here already: Is the IFC entities are case senstive?
It should be UPPERCASE. The proof is in the STEP ISO 10303 specification which I link to in that post.
If a vendor has implemented it to be case insensitive, they are being lenient, but it is not technically correct according to the spec.
Welcome to the BSI forums 
FYI IfcPerson is CapsCase, not camelCase.