Regular Expressions are a powerful method for matching the pattern of strings of text. This has particular relevance to text validation. In this recipe, we will add a simple regular expression to validate a URL which will require the text entered to begin with http://. This method does, however, allow any valid Regular Expression making it particularly flexible for validating any pattern that can be represented in a Regular Expression.
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', 'mytext5', 'URL');
$mform->addRule('mytext5', 'URL', 'regex', '^http://^', 'server');
When we test this new rule by entering a domain name instead of a full HTTP URL, our warning message will be displayed and once...
