Represents the "Subtype" entry of the projection 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 may take one of the following valid values:.

• O
• P

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 305, page 524.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 316, page 655.