parseStartTag(tagName, tag) {
    // Note: if 'mono' passed as tagName, there is a double check here. This is OK
    if (!this.mono && !this[tagName] && this.match(tag)) {
      this.setTag(tagName);
      return true;
    }

    return false;
  }
@param {string} tagName label for block type we are currently processing
@param {string|RegExp} tag string to match in text
@returns {boolean} true if the tag was processed, false otherwise