One child of a structure element (an entry of its K): another PdfStructureElement, a marked-content sequence
(PdfMarkedContentReference) or a whole PDF object (PdfObjectReference).
public abstract class PdfStructureItem
ISO 32000-2 §14.7.2, Table 355 (K), and §14.7.5.1.1: the last two are content items, the leaves of the tree.
kind:method, kind:property, kind:ctor. Press Esc to clear.ParentGets the structure element whose K holds this item, or null for a top-level element (a child of the root).