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: ...