required
textarea - This attribute specifies that the user must fill in a value before submitting a form. select - A Boolean attribute indicating that an option with a non-empty string value must be selected. input - This attribute specifies that the user must fill in a value before submitting a form. It cannot be used when the <strong>type</strong> attribute is <code>hidden</code>, <code>image</code>, or a button type (<code>submit</code>, <code>reset</code>, or <code>button</code>). The <a title="The :optional CSS pseudo-class represents any <input>, <select>, or <textarea> element that does not have the required attribute set on it." href="/en-US/docs/Web/CSS/:optional"><code>:optional</code></a> and <a title="The :required CSS pseudo-class represents any <input>, <select>, or <textarea> element that has the required attribute set on it." href="/en-US/docs/Web/CSS/:required"><code>:required</code></a> CSS pseudo-classes will be applied to the field as appropriate.