Yes, you guessed right, no need to ask any more,

You can get populated a combo box, depending on the value of other combo box, that is also populated at run-time by the value of other. Already lost? here is an example:

A usual requirement is to have a province combo populated depending on the country selected, until now easy, but you can go further and populate the cities combo box depending on the province selected before. Nice?

Here you have an image of the edit / add jsp of a real example:

Only cities of Alicante province are shown in the cities combo box. Only provinces of Spain are shown in the provinces combo box.

This way we can build better and easier CRUD portlets.

Here you have an XML definition file with a multi-chain validations. Just download and generate portlet. (MultiChainValidations.xml)

Remember, this option is only available for 6.1.x generations.

Liferay CRUD portlet development is getting easier every day.
Saludos, Jack.