Returns the structure element a marked-content identifier of the running content stream belongs to.
public PdfStructureElement? FindStructureElement(int mcid)
null when the document has no structure tree or the tree does not list it.ISO 32000-2 §14.7.5.2 and §14.7.5.4: an identifier in a page's content resolves through the page's StructParents; one in
a form XObject's content through the form's own StructParents (ContentStream).