Represents the "PS" entry of the number format dictionary object.

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

It contains a string representing a PDF string object.

The PDF specification states that this item assumes a value of "A single ASCII SPACE character (20h)" if no value has been provided.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 263, page 483.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 268, page 596.