How to Add HTML5 Placeholders to the WordPress Comment Form

html5placeholders.php

function my_update_comment_fields( $fields ) {

	$commenter = wp_get_current_commenter();
	$req       = get_option( 'require_name_email' );
	$label     = $req ? '*' : ' ' . __( '(optional)', 'text-domain' );
	$aria_req  = $req ? "aria-required='true'" : '';

	$fields['author'] =
		'<p class="comment-form-author">
			<label for="author">' . __( "Name", "text-domain" ) . $label . '</label>
			<input id="author" name="author" type="text" placeholder="' . esc_attr__( "Jane Doe", "text-domain" ) . '" value="' . esc_attr( $commenter['comment_author'] ) .
		'" size="30" ' . $aria_req . ' />
		</p>';

	$fields['email'] =
		'<p class="comment-form-email">
			<label for="email">' . __( "Email", "text-domain" ) . $label . '</label>
			<input id="email" name="email" type="email" placeholder="' . esc_attr__( "name@email.com", "text-domain" ) . '" value="' . esc_attr( $commenter['comment_author_email'] ) .
		'" size="30" ' . $aria_req . ' />
		</p>';

	$fields['url'] =
		'<p class="comment-form-url">
			<label for="url">' . __( "Website", "text-domain" ) . '</label>
			<input id="url" name="url" type="url"  placeholder="' . esc_attr__( "http://google.com", "text-domain" ) . '" value="' . esc_attr( $commenter['comment_author_url'] ) .
		'" size="30" />
			</p>';

	return $fields;
}
add_filter( 'comment_form_default_fields', 'my_update_comment_fields' );

I know this piece of code is 2y old, but just a warning to potential users of the snippet: Be sure to include the 'cookies' checkbox input that's added with the latest GDPR WordPress update v 4.9.5