[Catalyst] HTML::FormFu - how do constraints work?

[kakimoto at tpg.com.au]

hi all
 I have just posted out a question earlier as I could not get the
example for Tutorial::AdvancedCRUD::FormFu to work.

 I have also looked at the examples and put in the Constraint settings
in myapp.yml file but it does not work at all.

 Whilst I await for some help of you helpful folks to post regarding my
previous issue with Sqlite, 
can anyone tell me how do constraints work?

This is what I am guessing (and hoping):

- assume there's only an input textbox in the interface. Name = customerID
- a constraint has been set to 'Required' for the input text box.
- user clicks on submit without typing anything into the textbox.
- web browser returns a nice looking message saying something like, "
Input required for field, customerID"

 Is that faintly how it works?

thank you