Represents the "V" entry of the timespan dictionary object.

It is a required entry defined as part of the PDF 1.0 specification.

It contains a double representing a PDF numeric object.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 289, page 502.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 300, page 628.