General PDSEdit layer objects.
| ||PDSAttrObj||A PDSAttrObj represents a structure attribute object, which is a Cos dictionary or stream describing
attributes associated with a PDSElement. The attribute's data may be application-specific, suiting
the application that adds or extracts logical structure information. An attribute object can have a
revision number to indicate whether other applications have modified either the associated element
or the element's contents since the application created or modified the element.
| ||PDSClassMap||The PDSClassMap (or class map) associates class names with a set of attribute objects. A structural
element may have a list of names identifying the classes to which it belongs. Associated attributes
are shared by all structural elements belonging to a given class. There is only one class map per
document, associated with the PDSTreeRoot.
| ||PDSElement||PDSElement is the basic building block of the structure tree. It represents PDF structural elements,
which are nodes in a tree, defining a PDF document's logical structure.
| ||PDSMC||Portions of a page's contents may be wrapped with marked content operators. A PDSMC object represents
this marked content. A tag and an optional property list may be associated with a PDSMC. PDSMC is
identical to the PDFEdit class PDEContainer. PDSMC objects may be nested.
| ||PDSOBJR||An object reference (OBJR) is a reference to a PDF object. A PDSOBJR object references an entire Cos
dictionary or stream.
| ||PDSRoleMap||Each structure element must have a structure type. The definition of such types is application-specific.
In addition, PDF 1.3 defines a standard set of structure types for logical structure in PDF documents.
The role map (PDSRoleMap) maps application-specific element types to the standard element types that have
a similar function. There is only one PDSRoleMap per document, associated with the PDSTreeRoot.
| ||PDSTreeRoot||All logical structure information is in the structure tree, and the PDSTreeRoot is its root. There is
at most one PDSTreeRoot in each document.