Represents the "Ref" entry of the structure element dictionary object.

It is an optional entry defined as part of the PDF 2.0 specification.

It contains an array which contains StructureElementElements.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 323, page 558.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 355, page 721.