Represents the "Data" entry of the 3d node dictionary object.

It is an optional entry defined as part of the PDF 1.7 Extension Level 3 specification.

This property may contain one of two different types:.

1) A string representing a PDF string object.

2) A StreamElement.

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 312, page 538.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 323, page 671.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 9.47, page 58.