public function prepare()
    {
        if (null === $this->getAttribute('id')) {
            $this->setAttribute('id', 'pop-form');
        }
        if (null === $this->getAttribute('class')) {
            $this->setAttribute('class', 'pop-form');
        }
        if (count($this->columns) > 0) {
            foreach ($this->columns as $class => $fieldsets) {
                $column = new Child('div');
                $column->setAttribute('class', $class);
                foreach ($fieldsets as $i) {
                    if (isset($this->fieldsets[$i])) {
                        $fieldset = $this->fieldsets[$i];
                        $fieldset->prepare();
                        $column->addChild($fieldset);
                    }
                }
                $this->addChild($column);
            }
        } else {
            foreach ($this->fieldsets as $fieldset) {
                $fieldset->prepare();
                $this->addChild($fieldset);
            }
        }
        return $this;
    }