 On this interpretation, one considers reality exclusively between two temporal boundaries as being described by a classical field \(\phi\) that is a solution to the Klein-Gordon equation: specification of field values at both an initial and final boundary (as opposed to field values and their rate of change at only the initial boundary) constrains the field solutions between the boundaries. Wharton argues that constraining such fields at both an initial and a final boundary (or a closed hypersurface in spacetime) generates two strikingly quantum features: quantization of certain field properties and contextuality of the unknown parameters characterizing the field between the boundaries. (That there are unknown parameters before the imposition of the final condition is ensured due to the underdetermination of the classical field by specifying only the field values, and not their rate of change, in the initial data.)