code: function getConditionalComment(comment, modify, options) {
      var START_IF = '^\\s*\\[if .*\\]>',
          END_IF = '<!\\[endif\\]\\s*$',
          matchedStartIF = comment.match(new RegExp(START_IF)),
          matchedEndIF = comment.match(new RegExp(END_IF));
  
      if (comment.match(new RegExp(START_IF + '\\s*$')) || comment.match(new RegExp(START_IF + '<!\\s*$')) ||
              comment.match(new RegExp('^' + END_IF))) {
          return comment.trim();
      }
  
      if (matchedStartIF && matchedEndIF) {
          var start = matchedStartIF[0],
              end = matchedEndIF[0],
              modified = modify(comment.substring(start.length, matchedEndIF.index), options);
  
          return (start + modified + end).trim();
      }
  }
docs: Processes a conditional comment
  @param {String} comment
  @param {Function} modify
  @param {Object} options
  @returns {String|undefined}