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.

The Ref entry holds an array of indirect references to logically related structure elements, such as a footnote reference and its footnote, or a caption and the figure it describes.