Validating user input
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.
HTML5 input types are displayed as simple input fields in older web browsers that do not support these HTML5 features.
The example below shows these HTML5 input types in action.
This is particularly important for actions that are permanent or otherwise critical, but also when data cannot be automatically checked.
Forms frequently include required input that needs to be clearly identified using labels.
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.
Input errors, such as an incorrect email address, will be indicated using the web browser dialogs as in the previous example.
attribute allows the use of regular expressions to specify custom formats for the input.