Represents the "BaseVersion" entry of the developer extensions 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: 50, page 108.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 3.25b, page 25.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 49, page 140.