title: Do PUT request bodies have to contain an entire entity?
body: <p>When defining a PUT method on a resource is it required/standard/customary to include the entire definition of the resource (i.e. everything needed to create it) or is it also acceptable to send only updated fields?</p>
  
  <p>For example, if I have a resource with 10 attributes including one called quantity and I want to update the quantity to a specified value.  Is it acceptable to PUT only the quantity?</p>
  
  <p>What about the other 9 attributes?  Assuming each attribute could be updated individually, is it good practice to define the request body simply to have all 10 attributes as optional?</p>