docs: function isSymbol(t, v) {
    if (v === null) {
      return false;
    }
    // Native Symbol.
    if (t === 'symbol') {
      return true;
    }
    // 19.4.3.5 Symbol.prototype[@@toStringTag] === 'Symbol'
    if (v['@@toStringTag'] === 'Symbol') {
      return true;
    }
    // Fallback for non-spec compliant Symbols which are polyfilled.
    if (typeof Symbol === 'function' && v instanceof Symbol) {
      return true;
    }
    return false;
  }