Represents the "StructParents" entry of the page object object.

It is defined as part of the PDF 1.3 specification.

It contains an integer representing a PDF numeric object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 30, page 79.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 3.27, page 23.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 31, page 105.

The StructParents entry is an integer key into the document's parent tree that identifies the set of structure elements whose content appears on this page. It is required for pages that contain marked content referenced by the structure tree.