Represents the "RoleMap" 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 RoleMap entry holds a dictionary mapping non-standard structure type names to standard PDF type names. Readers follow the role map when they encounter an unrecognised element type.