ValidatePdfUa2Containment function

ValidatePdfUa2Containment walks the ParentIndex links of the flattened structure data and verifies that every element sits in an allowed parent for the ISO/TS 32005 containment model

Only a Document element may be a root, and a Document element may not have a parent; a parent index that is out of range or points at the element itself is also invalid

DocumentFragment and Title may only appear under Document, DocumentFragment, Part, Art, Sect, Div, or Aside

LI requires an L parent; Lbl requires LI, FENote, Note, or BibEntry; LBody requires LI

THead, TBody, and TFoot require a Table parent; TR requires Table, THead, TBody, or TFoot; TH and TD require TR

TOCI requires TOC or TOCI; Caption requires TOC, Table, Figure, Formula, or Aside

A MathML-namespaced element must sit inside a Formula element or inside another MathML-namespaced element

Every violation is reported as pvuaiNamespaceContainmentInvalid

• Namespace kinds are resolved with ClassifyPdfUaNamespace from the NamespaceUri recorded on each element
• ValidatePdfUa2StructureElements merges this rule family into the full PDF/UA-2 structure check