Problem with setting a default zero in form validation rule

[eluser]Mirge[/eluser]
There's nothing wrong with adjusting the value in a callback, but checking before your form validation is certainly a viable alternative.

BTW, if you return TRUE from your callback then you can't alter the value. See straight from documentation:

Code:

Note: You can also process the form data that is passed to your callback and return it. If your callback returns anything other than a boolean TRUE/FALSE it is assumed that the data is your newly processed form data.