In this recipe, we will add a rule that forbids all characters except alphabetic characters, that is, it allows only letters a-z in upper or lower case.
Please refer to the first recipe in this chapter for details on how to prepare a QuickForm web form which is the basis of this recipe.
Add the following code to our form definition in
validation_form.php, just after the field definition:
$mform->addElement('text', 'mytext7', 'Letters only'); $mform->addRule('mytext7', 'Letters only', 'lettersonly', null, 'client');
When we test out this rule by entering numeric characters, our warning message is displayed and we are not able to submit the form as seen in the following ...