title: What does this empty string mean?
body: <pre><code>&lt;script type="text/javascript"&gt;
  
          var step = 4;
  
          function expandPanel()
  
          {
  
              var panel = document.getElementById('panel');
  
              if ( panel.clientHeight &lt; (panel.originalHeight-step))
  
              {
  
                  //clientWidth
  
                  var h = panel.clientHeight + step;
  
                  panel.style.height = h+"px";
  
                  setTimeout("expandPanel()", 100); 
  
              }
  
              else
  
              {
  
                  panel.style.height = "";
  
                  var panelTitle = document.getElementById('panelTitle');
  
                  panelTitle.firstChild.nodeValue = 'Collapse';
  
  
  
              }
  
          }
  
  
  
          function collapsePanel()
  
          {
  
              var panel = document.getElementById('panel');
  
  
  
              if ( panel.clientHeight &gt;= step)
  
              {
  
                  var h = panel.clientHeight - step;
  
                  panel.style.height = h+"px";
  
                  setTimeout("collapsePanel()", 100);
  
              }
  
              else
  
              {
  
                  panel.style.display = 'none';
  
                  var panelTitle = document.getElementById('panelTitle');
  
                  panelTitle.firstChild.nodeValue = 'Expand';
  
              }
  
  
  
  
  
          }
  
  
  
          function changePanel()
  
          {
  
              var panel = document.getElementById('panel');
  
              if (!panel.style.height || 
  
                  (panel.style.display == 'none'))
  
              {
  
                  if (panel.style.display == 'none')
  
                  {
  
                      panel.style.display = '';
  
                      expandPanel();
  
                  }
  
                  else
  
                  {
  
                      panel.originalHeight = panel.clientHeight;
  
                      collapsePanel();
  
                  }
  
              }
  
          }
  
      &lt;/script&gt;
  </code></pre>
  
  <p>There is an empty string assigned to the <code>height</code> and <code>display</code> CSS properties (via CSSOM).
  What does it mean in this case? </p>