Represents the "Desc" entry of the standard structure attributes object.

It is an optional entry defined as part of the PDF 1.0 specification.

It contains a string representing a PDF string object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; page 593.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 347, page 608.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 382, page 784.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 348, page 609.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 383, page 785.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 349, page 610.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 384, page 785.

The Desc entry provides a text description of the structure element for accessibility, supplementing the element content with additional context not apparent from the visible text alone.