Represents the "FL" entry of the graphics state parameter dictionary object.

It is an optional entry defined as part of the PDF 1.3 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: 58, page 129.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 57, page 163.