Represents the "CYX" entry of the rectilinear measure 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.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 262, page 482.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 267, page 595.