title: how @usedby tag work in phpdoc
body: <p>By using @usedby tag hyperlink is not coming in documentation.</p>
  
  <pre><code>Class Content
  {
      /**
      * simple db class variable
      * @access public
      */
      var $_db=null; // db
      /**
      * s3 class instance
      */
      private $_s3=null; //  s3
      /**
      * application variable array for creating instance of each object 
      * @var array
      * @usedby Content::upload() this is compared 
      */
      public $application=array(
          'image'=&gt;array(
                  'createthumb'=&gt;'createimagethumb'
                  ),
          'audio'=&gt;array(
                  'createthumb'=&gt;'createaudiothumb'
                  ),
          'video'=&gt;array(
                  'createthumb'=&gt;'createvideothumb'
                  ),
          'link'=&gt;array(
                  'createthumb'=&gt;'createlinkthumb'
                  )
          );
  /**
      * for uploading new content or you can say add new content :)
      *
      * @return json of new contents 
      **/
      function upload()
      {
          if ($_POST['gibname']=='' or $_POST['gibview']=='') {
              $msg=createmessage(false, 'Please enter gibname and gib view where you want to place content');
          }
          $maxFileSize = 100 * 1024 * 1024;   // Max file size 100 MB
          $thumb = $status =$imgWidth = $imgHeight = '';
          $headers = apache_request_headers();        // Get file size from Apache headers
          $fileSize=(int)$headers['Content-Length'];
          $fileType = (string)$headers['Content-Type']; // Get MIME type from Apache headers
          $clientfileType = $fileType;
          if (preg_match("/^multipart/", $fileType) ) $fileType = $_FILES['qqfile']['type'];
          if ($fileType=='application/octet-stream') $fileType="video/flv";
          if ($fileSize == 0) {
              return array('success'=&gt;false, 'error'=&gt;"File is empty.");
          }               
          if ($fileSize &gt; $maxFileSize) {
              return array('success'=&gt;false, 'error'=&gt;"File is too large.");
          }
          $pathinfo = pathinfo($_REQUEST['qqfile']);        // Put data of pathinfo() array into $pathinfo    
          $filename = $pathinfo['filename'];// Get file name - eg: myphoto
          $ext = $pathinfo['extension'];        // Get extension - eg: .jpg
          if ($ext=='') $ext=substr(strrchr($_FILES['qqfile']['name'], '.'), 1);
          $originalName = $filename.'.'.$ext;
          $randName = uniqid();               // Generate unique id for the current object
          $fileTempName =  $randName . '.' . $ext;    // Unique file name with extension
          $fullTempName = "uploads/".$fileTempName;        // Set temp directory where files will be written temporarily        // Complete temp file name and path
          if (!preg_match("/^multipart/", $clientfileType)) { // Upload the file to temp directory on .net server
              $input = fopen("php://input", "r");
              $fp = fopen($fullTempName, "w");
              while ($data = fread($input, 1024)) {
                  fwrite($fp,$data);
              }
              fclose($fp);
              fclose($input);         
          } else
              move_uploaded_file($_FILES["qqfile"]["tmp_name"], $fullTempName);
          $objecttype=mb_substr($fileType,0,-mb_strlen(strrchr($fileType,"/")));
          //for uploading of link url is neccesssary
          if ($_POST['url']!='' or $_POST['refername']!='') {
              $objecttype="link";
              $url=$_POST['url'];
              $filename=$_POST['filename'];
          } else {
              $url=CLOUDFRONT.$fileTempName;
              $filename=$fileTempName;
          }
          if (class_exists($objecttype) &amp;&amp; $_POST['refername']=='') {
              $object=new $objecttype();
              $str=$this-&gt;application[$objecttype]['createthumb'];
              $thumb=$object-&gt;{$str}($fullTempName,$fileType);
              $thumbnail=$thumb['thumb'];
              $preview=$thumb['preview'];
              $imgWidth=$object-&gt;imagewidth;
              $imgHeight=$object-&gt;imageheight;
              $resize=$object-&gt;resize;
          }
  }
  </code></pre>
  
  <p>While @usedby is not the warning is coming telling unknown tag .
  phpdocumentor version is 1.4.3
  why it is saying the unknown tag .</p>