Represents the "BBox" entry of the shading dictionary object.

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

It contains a RectangleElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 78, page 183.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 77, page 228.

The BBox rectangle clips the shading to a region in shading space. Nothing is painted outside this box. Using a tight BBox can improve rendering performance by limiting the area the renderer must process.