[This is preliminary documentation and is subject to change.]
Constructs a path to this IElementDef object, comprised of the names of
its ancestry delimited by an underscore. The path can be used to lookup
an IElementDef object via the LookupElementDef(String) method.
Note the strings used in the path generated by this method are not
necessarily the same as the element or attribute tag names used in SIF
XML messages. Rather, they are version-independent names typically equal
to the tag name of the element in SIF 1.0r1.
A path string (e.g. "StudentPersonal_RefId")