This is done by using validation attributes on form elements.
Note that ARIA is an independent specification that's not specifically related to HTML5.
Add the "Validate" link below to your bookmark (or "favorites") toolbar to create a bookmarklet.
To run DOM Validator, enter the following Usage: perl [options] This program invokes the DOM Parser, and then prints any errors to STDERR.
Form validation helps us to ensure that users fill out forms in the correct format, making sure that submitted data will work successfully with our applications.
This lets you use Java Script code to establish a validation failure other than those offered by the standard constraint validation API.