Represents the "Subtype" entry of the postscript xobject 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.

This item must always be provided and must always take the value "PS".

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 88, page 202.