This is a newbie question.

What are the general things to pay attention too when handling data that were sent from a form?

The form has a few text widgets, a couple of comboboxes, a hidden text field, and two jQuery datepickers.

I was thinking of writing a loop in PHP to check for the length, and possibly the pattern using regexes.

If you know of a good pratical article that explains how to handle forms safely, I'm interested.

Thank you.