code: function atrule() {
      if (css[0] != '@') return;
  
      return atkeyframes()
        || atmedia()
        || atcustommedia()
        || atsupports()
        || atimport()
        || atcharset()
        || atnamespace()
        || atdocument()
        || atpage()
        || athost()
        || atfontface();
    }
docs: Parse at rule.