Represents the "DS" entry of the field dictionary object.

It is an optional entry defined as part of the PDF 1.5 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; Table: 220, page 432.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 226, page 527.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 222, page 434.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 228, page 529.

The default style string is a CSS-like specification used as the default formatting for rich-text content in text fields when no explicit style is present in the rich content itself.