anchor.diff:      <p>
         Once all of this is done and instructor selects an exercise from a tree
         view, a URL of the selected exercise is returned back to the tool
  -      Consumer. In Canvas, the returned URL is added under Submission Tool URL
  +      Consumer. In Canvas, the returned URL is added under Submission Tool URL,
         as shown in the image below:
         <div class="text-center">
           <%= image_tag "OpenDSA/submission_tool_url.png", style:'width:40%' %>
  
positive.code:   <br> <br>
  
    Within the <em>lti_authorize!</em> endpoint, OpenDSA creates a tool
    provider object from the authentication object created above and throws an
    error and returns in case the key and secret do not match.<br><br>
  
    <pre>
      def lti_authorize!
  
negative.code: 
    If the key and secret match, then within the same 'lti_authorize!' endpoint
    OpenDSA checks if the request is valid or not, or if the timestamp on the
    request is too old. If so, then OpenDSA returns an error. Otherwise, it
    returns "<em>true</em>" to the <em>launch_ex</em> endpoint, which means the
    request is valid.
    <br><br>
  
    <pre>
  