Require just the zip code?

We'd like to able to require just the zip code field of an address. Is this possible, using the pre-built address field?

This is a form it would be good to do on:
http://www.anandala.org/free-book-chapters/

Thanks!

Hi Alex, thanks for your answer. That's great to know. I see now that the hooks are documented.

Looks like I would use gform_pre_submission to run a validation on the zip code and -- somehow?? -- stop the form?

Superb. Thanks, Alex.

Is there a complete list of filters anywhere?

Hi all,

Thought I'd add a note for other n00bs like me:

1) when I first copied this example, I somehow got rid of the following line -- that will break things:

$form = $validation_result["form"];

2) to get access to the submitted data, you have to access it via the regular HTTP $_POST["input_name"] PHP server variable (where 'input_name' is probably 'input_1', etc.), b/c at this stage of processing, the $form does not seem to have the submitted values set.

so, my full, working test example is:

add_filter('gform_validation', 'custom_validation');

function custom_validation($validation_result){

    $form = $validation_result["form"];

    // if value of first field name != 'peter'
    if( strcmp($_POST["input_1"],"peter")!=0 ){  

        // then mark this submission invalid
        $validation_result["is_valid"] = false;

        // mark the errant field [the first (0th) field]
        $form["fields"][0]["failed_validation"] = true;

        // and put in an explanatory message to the user on how to fix
        $form["fields"][0]["validation_message"] = "This first field must have the value 'peter'.";
    }

    // update the form in the validation result with the form object you modified
    $validation_result["form"] = $form;

    return $validation_result;
}