D link validating
This lets you use Java Script code to establish a validation failure other than those offered by the standard constraint validation API.
The message is shown to the user when reporting the problem.
Validation attributes allow you to specify rules for a form input, such as whether a value must be filled in; the minimum and maximum length of the data; whether the data needs to be a number, an email address, or something else; and a pattern that the data must match.
If the information is correct, the application allows the data to be submitted to the server and (usually) saved in a database; if the information isn't correct, it gives you an error message explaining what needs to be corrected.
Form validation can be implemented in a number of different ways.
We refer to the value matched for subexpression as $.
For example, matching the above expression to It depends on your definition of valid. The quick approach would be to use preg_match to test the url against a good regular expression to validate it's of the correct format.