Represents the "ClassMap" entry of the structure tree root object.

It is an optional entry defined as part of the PDF 1.0 specification.

It contains an Element.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 322, page 557.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 354, page 720.

The ClassMap entry holds a dictionary mapping class names to attribute objects. Structure elements reference class names in their C entries to inherit the corresponding attributes.