anchor.diff:      <strong>content_item_return_url=</strong> [URL] (Required) <br>
       <p>
         This field contains a URL where Tool Provider redirects the user back to
  -      Tool Consumer.
  +      the Tool Consumer.
  +    </p>
  +
  +    <strong>accept_unsigned=</strong> false | true (Optional)
  +    <br>
  +    <p>
  +      This field indicates whether the the Tool Consumer accepts an unsigned
  +      return message or not.
  +    </p>
  +
  +    <strong>accept_multiple=</strong> false | true (Optional)
  +    <br>
  +    <p>
  +      accept_multiple indicates if user can select multiple content items or not.
  +    </p>
  +
  +    <strong>accept_copy_advice=</strong> false | true (Optional)
  +    <br>
  +    <p>
  +      This field indicates if the Tool Consumer will make a local copy of a
  +      content item. Tool Providers can send <em>expiresAt</em> parameter to let
  +      the Tool Consumer know that the item will expire on that date.
       </p>
   
       <strong>accept_unsigned=</strong> false | true (Optional)
  
positive.code:     <strong>data=</strong> [Same as received] (Optional)
      <br>
      <p>
        If Tool Consumer sent this parameter in original request, then Tool
        Provider should return it as is to TC.
      </p>
  
      <strong>lti_msg=</strong> [Message to be displayed] (Optional)
  
negative.code:       message or not.
      </p>
  
      <p>
        Along with the fields mentioned above, the Tool Consumer can also send
        additional fields like text, title, data, auto_create (to indicate if
        content items returned by the Tool Provider would be automatically
        persisted) and other parameters about the Tool Consumer and the user.
      </p>
      <br>
  
      <p>
        Once content item(s) has been selected, Tool Provider should redirect
        the user to the Tool Consumer by sending POST request. It may send the
        following parameters in the request:
      </p>
  
      <strong>lti_message_type=</strong> ContentItemSelection (Required)
  