This property is H5 newly added attribute is a Boolean attribute, the default is ture, field specifies before submitting the form must be entered
This attribute applies to input type (type = "") are:
- text
- search
- url: Enter the URL field (Uniform Resource Locator: it is popular URL)
- tel: telephone number entry field
- email: email address
- password: password input field
- date pickers
- number: Digital input field
- checkbox: check box
- radio: radio button
file: file selection field and the "Browse ..." button, for file uploads
In H5, concerned with such may be required <input type = "text" required />
在XHTML中，required用法为<input type="text" required="required" />