Represents the "Assets" entry of the richmediacontent dictionary object.

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

It contains a NameTreeNodeElement containing FileSpecificationElements.

For definitive details see:.

Adobe Supplement to the ISO 32000, BaseVersion: 1.7, ExtensionLevel: 3; Table: 9.51, page 86.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 341, page 704.

The Assets entry is a name tree mapping asset names to file specifications. Each file specification references one embedded media file; configurations and instances reference these assets by their name keys.