code: function (content, block, target, type, attbs, alternateSearchPaths, handler) {
      var linefeed = /\r\n/g.test(content) ? '\r\n' : '\n',
          lines = block.split(linefeed),
          ref = '',
          indent = (lines[0].match(/^\s*/) || [])[0],
          ccmatches = block.match(regcc),
          blockContent = lines.slice(1, -1).join('');
  
      target = target || 'replace';
  
      if (type === 'css') {
  
          // Check to see if there are any css references at all.
          if( blockContent.search(regcss) !== -1 )
          {
              if(attbs) {
                ref = '<link rel="stylesheet" href="' + target + '" ' + attbs + '>';
              } else {
                ref = '<link rel="stylesheet" href="' + target + '">';
              }
          }
  
      } else if (type === 'js') {
  
          // Check to see if there are any js references at all.
          if( blockContent.search(regscript) !== -1 )
          {
              if(attbs) {
                ref = '<script src="' + target + '" ' + attbs + '></script>';
              } else {
                ref = '<script src="' + target + '"></script>';
              }
          }
  
      } else if (type === 'remove') {
          ref = '';
      } else if (handler) {
        ref = handler(blockContent, target, attbs, alternateSearchPaths);
      }
      else {
        ref = null;
      }
  
      if(ref != null) {
        ref = indent + ref;
  
        // Reserve IE conditional comment if exist
        if (ccmatches) {
          ref = indent + ccmatches[1] + linefeed + ref + linefeed + indent + ccmatches[2];
        }
  
        return content.replace(block, ref);
      }
      else { return content; }
    }
docs: useref and useref:* are used with the blocks parsed from directives