function filtering(cat)
{
  if(cat == sel_cat) return;
  document.getElementById('tab_'+ sel_cat).style.backgroundColor='#e3e3e3';
  document.getElementById('tab_'+ cat).style.backgroundColor='#cdcdcd';
  
  var e = document.getElementById('filter_'+ sel_cat);
  var el = document.getElementById('filter_'+ cat);
  
  el.style.display ='';
  e.style.display = 'none';

  sel_cat = cat;
  loadCategoryList();
  if(cat =='construction')
  { 
    loadCategorySelector('1','3584.aspx?alttemplate=CAD Category');
    try { 
      document.getElementById('placeholder_2').innerHTML ='<select size="4"></select>'; 
      document.getElementById('placeholder_3').innerHTML ='<select size="4"></select>'; 
    }
    catch(e) {;}
   
  }
}