This class represents the appearance dictionary. This is definitively detailed in:.

The ISO PDF Specification, ISO 32000-1:2008 PDF 1.7; Table: 168, page 389.

The ISO PDF Specification, ISO 32000-2:2017 PDF 2.0; Table: 170, page 472.

System.Object
    WebSupergoo.ABCpdf14.Elements.Element
       WebSupergoo.ABCpdf14.Elements.AppearanceElement

An appearance dictionary holds the form XObject streams defining how an annotation looks. The three entries N, R, and D correspond to the normal, rollover, and down visual states.

Each entry can be either a single form XObject or a sub-dictionary of named form XObjects, used when the annotation has multiple appearance states such as a checkbox with on and off appearances.

The current appearance state is selected by the AS entry in the parent annotation dictionary.