heading(text, level, raw, slugger) {
    if (this.options.headerIds) {
      const id = this.options.headerPrefix + slugger.slug(raw);
      return `<h${level} id="${id}">${text}</h${level}>\n`;
    }

    // ignore IDs
    return `<h${level}>${text}</h${level}>\n`;
  }
@param {string} text
@param {string} level
@param {string} raw
@param {any} slugger