Represents the "O" entry of the 3d node dictionary object.

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

It contains a double representing a PDF numeric object.

It should have a minimum value of 0 and a maximum of 1.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 312, page 538.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 323, page 671.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 9.47, page 58.