The global FaceBase element is the head of a substitution group whose members define faces. Any element that is a member of the group may be substituted for the FaceBase element anywhere the FaceBase element may be used in an instance file.
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 turned attribute shows if the face orientation must be reversed from the orientation of the underlying surface. If the value is true, the face orientation must be opposite the surface orientation. If the value is false, the two orientations must be the same.
Source
<xs:element name="FaceBase" type="FaceBaseType" abstract="true"><xs:annotation><xs:documentation>The global FaceBase element is the head of a substitution group whose members define faces. Any element that is a member of the group may be substituted for the FaceBase element anywhere the FaceBase element may be used in an instance file.</xs:documentation></xs:annotation></xs:element>