code: function handleOnTag(file, tagName, replaceTagName) {
      let tags = file.tags;
      tags || (tags = file.tags = {});
      if (replaceTagName && tags.hasOwnProperty(replaceTagName)) {
          delete tags[replaceTagName];
      }
  
      tags[tagName] = true;
  }
docs: On tag handler
  
  @inner
  @param {Object} file the template file
  @param {string} tagName the tag name to encounter
  @param {string=} replaceTagName the old tag name to replace