Adds an attribute object owned by the namespace ns (O NSO) to the element's A entry.
public PdfAttributeObject AddAttributes(PdfStructureNamespace ns)
The owning namespace; it is listed in the root's Namespaces when it is not yet.
ISO 32000-2 §14.7.6.1, Table 360 (NS, PDF 2.0); ISO/TS 32005 §6.