Represents the "S" entry of the output intent dictionary object.

It is a required entry defined as part of the PDF 1.0 specification.

It contains a string representing a PDF name object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 365, page 633.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 401, page 814.

The S entry names the output intent subtype identifying the standard: GTS_PDFX for PDF/X, GTS_PDFA1 for PDF/A, and ISO_PDFE1 for PDF/E.