Represents the "A" entry of the link annotation object.

It is an optional entry defined as part of the PDF 1.1 specification.

It contains an ActionElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 173, page 394.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 176, page 479.