title: RESTful API: What METHOD/HEADER combo to use for validation-only
body: <p>I would like my API to have a validation-only request. For example, if I have a URL such as:</p>
  
  <pre><code>http://api.somesite.com/users/12345
  </code></pre>
  
  <p>and the user is filling out a form of information on a client that I will eventually PATCH/PUT/POST to that resource. As the user is filling out the form, I might want to send over their partially-complete updated representation over to the server periodically so I can display realtime validation of their input (e.g., "That username is already taken", "That password is too short").</p>
  
  <p>There isn't a standard HTTP METHOD or HEADER that seems to allow for this behavior on that same resource. It seems my options are:</p>
  
  <ol>
  <li>Create a new subordinate resource for validation</li>
  <li>Use a custom header (x-somesite-validation-only) and PUT indicating that I want to validate but not save</li>
  </ol>