Validating a website
For example, telephone numbers are written with different separators and digit groupings.
Your form will be easier to use if it can interpret multiple notations. For example, postal codes aren't confined to just numbers in some countries, so using an can easily become a problem for many of your website users.
Also, the attribute can be added to form controls, to programmatically indicate that they are required.
Most current web browsers support this attribute and will communicate missing required input to the user, using standard web browser dialog mechanisms.
Similarly, the “Number” input field may be displayed with buttons to increase or decrease the number incrementally.Note that the label also displays “(required)”, to inform users that don’t use assistive technology or use older web browsers that do not support the HTML5 attribute informs assistive technologies about required controls so that they are appropriately announced to the users (as opposed to validating the input).Most current web browsers automatically set its value to .If your web browser supports HTML5, it will not allow you to submit the form without entering text into the input field.Instead, it will display a message that is generated by the web browser itself.