title: Creating a resource that can have multiple representations
body: <p>Say I have a Widget resource which is made up of a Thingy and a Dooda.
  Thingys and Doodas come in various types and the combination of Thingy type and Dooda type will determine exactly what properties a Widget will have.
  Whilst I understand that in order to create a Widget I should send a complete representation of the resource, the potential combination of Thingys and Doodas is numerous so it is impractical to send all the possible properties in one Widget object.</p>
  
  <p>Therefore in order to create a Widget I only require those properties to be sent that are defined by the combination of Thingy and Dooda.
  What is the best way to communicate to the client the definition of the representation to send?</p>
  
  <p>My first thoughts are to provide an endpoint to which the client can send the Thingy/Dooda type combination and receive back a blank 'template' representation of the Widget which defines which properties are required, or is there a better way to handle this situation?</p>