Apply the mapping to a Document, creating one or more Objects
and assigning values to fields in the Object(s), recursing
through the Document to generate an object tree.
Apply the ordering to an XML element, using values of XML
attributes and other Nodes to set fields in the object,
create child objects, and so forth, recursively.
These are a subset of what rule [28] calls ExprToken but with the
addition of left and right curly brackets (braces), the colon, the
dollar sign, and possibly other symbols.