code: public function isa($type, $option = null)
      {
          // "bool" was kept for backward compatibility
          if ($type === 'bool') {
              $type = 'boolean';
          }
          $this->isa = $type;
          $this->isaOption = $option;
  
          return $this;
      }
docs: Value Type Setters.
  
  @param string $type   the value type, valid values are 'number', 'string',
  'file', 'boolean', you can also use your own value type name.
  @param mixed  $option option(s) for value type class (optionnal)