The optional size attribute defines a recommended size for visualization of an infinite drawable element such as plane, cylinder, axis, etc., or objects without explicit geometric parameters (e.g. coordinate system).
The optional transparency attribute defines the transparency property of a model entity.
Source
<xs:complexType name="AuxiliaryBaseType" abstract="true"><xs:annotation><xs:documentation>The AuxiliaryBaseType is the abstract base type for all auxiliary object types.</xs:documentation></xs:annotation><xs:complexContent><xs:extension base="DrawableBaseType"/></xs:complexContent></xs:complexType>