The published OCX Schema

Abstract class: A reference to a bounded object with limted extent. BoundedRef has the following child elements:

Child	Namespace	Type	Use	Cardinality	Choice	Description
BoundingBox	ocx	ocx:BoundingBox_T	opt.	[0, 1]	False	The definition of a bounding box in space using two positions.The bounding box defines the parent extent.

BoundedRef has the following attributes:

Attribute	Namespace	Type	Use	Default	Fixed	Description
localRef	ocx	xs:IDREF	opt.			A rference to a unique ID within the scope of this XML file. Ether a localRef or a GUIDRef shall be provided, or both. The schema will check this by the assertion: test=“(@localRef and not(@ocx:GUIDRef)) or (not(@localRef) and @ocx:GUIDRef) or (@localRef and @ocx:GUIDRef)”.
GUIDRef	ocx	Restriction of type ocx:guid	opt.			A globally unique ID referring to an entity in the authoring application. The sending application creates and holds the GUID. Used to establish a unique reference to an entity persistent between applications. Ether a localRef or a GUIDRef shall be provided, or both. The schema will check this by the assertion: test=“(@localRef and not(@ocx:GUIDRef)) or (not(@localRef) and @ocx:GUIDRef) or (@localRef and @ocx:GUIDRef)”.