An HTML form with a required input field:
The required attribute is a boolean attribute.
When present, it specifies that an input field must be filled out before submitting the form.
Note: The required attribute works with the following input types: text, search, url, tel, email, password, date pickers, number, checkbox, radio, and file.
The numbers in the table specify the first browser version that fully supports the attribute.
The required attribute is new in HTML5.
In XHTML, attribute minimization is forbidden, and the required attribute must be defined as <input required="required" />.