To be honest, I'm not completely sure. I'm reading a document (which is unfortunately proprietary, otherwise I would share) that talks about binding XML data elements to form objects. Maybe the code used to do such binding is not in XML but the data elements are described as being XML data.
The problem this document describes is that when the XML data becomes encrypted, it is difficult to correctly bind the form object to the correct data element. It proposes a solution, and then two sides argue whether that solution is involves ONLY implicit binding, or if the solution can be interpreted broadly enough to include explicit binding. I'm not sure what explicit or implicit binding conceptually and neither side provides a definition for either term.