Returns true if this DSM element is a pseudo-element and false otherwise.

Pseudo-elements are technically not XML elements, however, most of them are associated with other XML DOM nodes (for example, pseudo-elements with '#TEXT' name represent DOM Text nodes).
Some pseudo-elements may be not associated with a particular XML file at all. For instance, #DOCUMENTS element represents all open XML documents, and #CUSTOM elements may be used to represent any data items as "elements" and "attributes", which allow operating with them. (Note that most of template components, functions and properties can work only with elements and attributes!)
DocFlex/XML extends the XML DOM and treats all such objects as generic DSM elements, the same way as the normal XML elements. However, this property allows you to distinguish this when needed.

For more details about pseudo-elements, see DocFlex/XML documentation.