code: function inspect(engine) {
    var inspect = ['"' + engine.name + '"'];
    var exts = utils.arrayify(engine.options.ext).join(', ');
    inspect.push('<ext "' + exts + '">');
    engine.inspect = function() {
      return '<Engine ' + inspect.join(' ') + '>';
    };
  }
docs: Add a custom inspect function onto the engine.