Represents the "CapHeight" entry of the font descriptor object.

It is 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: 122, page 282.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 120, page 342.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 124, page 285.

Cap height is the distance from the baseline to the top of a flat capital letter such as H, measured in glyph space. It is used for aligning mixed-size text and for font substitution decisions.