There is no point returning a value from an on Change handler - it's not used for anything.
Because the code is stored on the server, server-side validation requires a roundtrip to the server.
The script has a catalog of almost all the common validation types built-in.
The idea is to create a set of “validation descriptors” associated with each element in a form.
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.