No common pattern for XML xor and cardinality

Comparing e.g. Shape element:

Name	Type	Cardinality	AppliedStereotypes	Description
polyline	Polyline	0..1	xor, XSDelement	Polyline property of a shape.
clothoid	Clothoid	0..1	xor, XSDelement	Clothoid property of a shape.
nurbs	Nurbs	0..1	xor, XSDelement	NURBS property of a shape.

and TrajectoryRef

Name	Type	Cardinality	AppliedStereotypes	Description
trajectory	Trajectory	1..1	xor, XSDelement	A trajectory definition.
catalogReference	CatalogReference	1..1	xor, XSDelement	Reference to a trajectory in a catalog.

they differ in terms of cardinality. And for no good reason, what I can see. They both should have one and only one of the sub elements. So the question is: Is one of the formats more correct?

And in that case should classes with the XML "Choice" element be aligned? On the other hand I guess that would be a problem w.r.t. backward compatibility.

At least it would be good to define preferred format for new classes to be added in 1.2 forward.