For ‘selections’ like drop down and radio group, use an appropriate validation like ‘dontselect’ or ‘selone_radio’.
This validation descriptor is valid only for drop down lists.
If so, it allows it to be submitted to the server and (usually) saved in a database; if not, it gives you error messages to explain what you've done wrong (provided you've done it right).
There are no required external dependencies at all!
An email address must contain at least a ‘@’ sign and a dot (.).
Also, the ‘@’ must not be the first character of the email address, and the last dot must at least be one character after the ‘@’ sign.
For example, you can have an input field that should not be empty, should be less than 25 chars and should be alpha-numeric. In some dynamically programmed pages, it may be required to change the validations in the form at run time.
In other words, in order to validate a field, you just associate a set of validation descriptors for each input field in the form. For such cases, a function is included which clears all validations in the validator object. Note that this validation if for fields like Textbox and multi-line text box.