protected function addCheckbox($tag)
{
if (!isset($this->checkboxes[$tag->getName()])) {
$this->widgets[] = $tag;
$this->checkboxes[$tag->getName()] = count($this->widgets) - 1;
} else {
$index = $this->checkboxes[$tag->getName()];
if (!is_a($this->widgets[$index], 'SimpleCheckboxGroup')) {
$previous = $this->widgets[$index];
$this->widgets[$index] = new SimpleCheckboxGroup();
$this->widgets[$index]->addWidget($previous);
}
$this->widgets[$index]->addWidget($tag);
}
}