anchor.diff:      return modArr;
     };
   
  +  function cdnModArr(uri, modArr){
  +    var modStr, mods, i;
  +
  +    if (uri && urlDomain(uri.host) === 'cdn'){
  +      modStr = uri.path.split('/')[1];
  +      if (hasModifierStr(modStr)){
  +        mods = modStr.split('-');
  +
  +        // if no mods are specified then use those from the existing url
  +        if (modArr.length === 0){
  +          modArr = mods;
  +        }
  +
  +        // if there are mods specified then only add any existing external
  +        // source or filter modifiers
  +        else {
  +          for (i=0; i < mods.length; i++){
  +            if (mods[i][0] === 'e' || mods[i][0] === 'f'){
  +              modArr.push(mods[i]);
  +            }
  +          }
  +        }
  +      }
  +    }
  +
  +    return modArr;
  +  };
  +
     function buildPath(uri, modifiers){
       if(uri){
         switch(urlDomain(uri.hostname)){
  +        case 'cdn':
  +          return cdnObject(uri);
  +          break
           case 's3':
             return s3Object(uri);
             break;
  
positive.code:   };
  
    function urlDomain(host){
      var domain = 'other';
      if (/s3.amazonaws.com/i.test(host)){
        domain = 's3';
      }
  
negative.code:       domain = 'facebook';
      }
      return domain;
    };
  
    // Get the path of an already IR'd url, basically make sure we remove the
    // modifier string if it is present
    function cdnObject(uri){
      var parts = uri.pathname.split('/');
  
      // test to see if there is an existing modifier string in place
      if (hasModifierStr(parts[1])){
        return '/' + parts.slice(2).join('/');
      }
  
      return uri.pathname;
    };
  
    function hasModifierStr(part){
      var items, i, item, key, value, flag, v;
  
      items = part.split('-');
      for (i in items){
        item = items[i];
        key = item[0];
        value = item.slice(1);
        flag = false;
        v = modSet(key);
        if (v){
          if (v.values){
            flag = true;
          } else {
            flag = 1 * value > 0;
          }
        }
        if (flag){
          return true;
        }
      }
  
      return false;
    };
  
    function s3Object(uri){
  