Represents the "OC" entry of the alternate image dictionary object.

It is an optional entry defined as part of the PDF 1.5 specification.

It contains an OptionalContentGroupElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 91, page 212.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 89, page 261.

The OC entry associates this alternate with an optional content group or membership dictionary. The alternate is a candidate for use only when the associated content group is on.