Existing Wording: The base definition for elements defined as part of a resource.

Comment:

What is an "element" vs a "backbone element?" In 1.20.0, the definition of Element ("The base definition for all elements contained inside a resource") sounds almost the same as the definition for Backbone Element ("The base definition for elements defined as part of a resource"). What is the distinction between elements "contained inside a resource" vs "elements defined as part of a resource?"