title: HTTP response code when resource creation POST fails due to existing matching resource
body: <p>Imagine we have an API where a new Employee can be created through a POST to </p>
  
  <pre><code>www.example.com/api/employees
  </code></pre>
  
  <p>An employee could be described as,</p>
  
  <pre><code>{
    name: "John Smith",
    tax_number: "ABC123"
  }
  </code></pre>
  
  <p>The tax number is universally unique for all humans. If a create were made, and a record already existed in which the name and tax number matched an existing record, it is safe to assume the requester would like a reference to that record returned (with it's internal id and other data the client may not have, eg. created at, updated at).</p>
  
  <p>What would the HTTP status code be for returning that resource? I suppose a redirect could be used with a return of just the id, but I'd prefer to enclose the entire object in the response.</p>
  
  <p>This case is unique to a simple duplicate error, in the sense that if a duplication is attempted it means the record you wish to create already exists- as opposed to it conflicting with an existing record. </p>