code: function _interfaceish(node, print) {
    print.plain(node.id);
    print.plain(node.typeParameters);
    if (node["extends"].length) {
      this.push(" extends ");
      print.join(node["extends"], { separator: ", " });
    }
    if (node.mixins && node.mixins.length) {
      this.push(" mixins ");
      print.join(node.mixins, { separator: ", " });
    }
    this.space();
    print.plain(node.body);
  }
docs: Prints interface-like node, prints id, typeParameters, extends, and body.