Represents the "First" entry of the outline dictionary object.

It is defined as part of the PDF 1.0 specification.

It contains an OutlineItemElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 152, page 368.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 150, page 442.

This entry points to the first visible item at the top level of the outline tree. Following the chain of Next references from this item visits all top-level items in order.