Represents the "OP" entry of the rendition action object.

It is defined as part of the PDF 1.0 specification.

It contains an integer representing a PDF numeric object.

It should have a minimum value of 0 and a maximum of 4.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 214, page 428.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 218, page 520.