Represents the "Subtype" entry of the 3d animation style dictionary object.

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

It contains a string representing a PDF name object.

The PDF specification states that this item assumes a value of "None" if no value has been provided.

This item may take one of the following valid values:.

• None
• Linear
• Oscillating

For definitive details see:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 301, page 517.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 312, page 646.