Represents the "S" entry of the source information dictionary object.

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

It contains an integer representing a PDF numeric object.

The PDF specification states that this item assumes a value of 0 if no value has been provided.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 355, page 623.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 391, page 803.