I have followed the guide here and created a custom tab on CMS Pages:
I now want to add a Category tree to this custom page. I have an answer here but I'm confused by this step:
In your form file where you add the tabs of your custom entity add this also:
$this->addTab('categories', array( 'label' => Mage::helper('[module]')->__('Associated categories'), 'url' => $this->getUrl('*/*/categories', array('_current' => true)), 'class' => 'ajax' ));
I am not sure what is meant by "form file". Can anyone point me in the right direction?