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

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

It contains an array which contains FileSpecificationElements.

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 AF entry holds an array of file specification dictionaries for files associated with the document logical structure as a whole, rather than with any specific page or object.