Writing forms in symfony templates is facilitated by the standard form helpers and their smart options. When you design a form to edit the properties of an object, the object form helpers simplify the task a great deal. The validation files, validation helpers, and repopulation feature reduce the work necessary to build a robust and user-friendly server control on the value of a field. And even the most complex validation needs can be handled, either by writing a custom validator or by creating a validateXXX() method in the action class.
The definitive guide of Symfony 1.0