WordPress Genesis searchform with label and hook for genesis_header_right

wpacc_search_form_header.css

.prefix-hidden {
	background-color: #fff;
	border: 1px solid #000;
	display: block;
	font-size: 1em;
	left: -1000em;
	padding: 0.8em;
	position: absolute;
	z-index: 10;
}
.hidden:focus, .hidden:active {
	top:1em;
	left:1em;
	z-index:1000;
	color: #1E6891;
}

wpacc_search_form_header.php

<php
/**
* WordPress Genesis Accessible searchform for the header
* Rian Rietveld - rrwd.nl
* Add this to the functions.php in your child theme for the Genesis Framework by StudioPress.
* This function replaces the search form with a more accessible one by adding a hidden label
*/

add_action ('genesis_header_right' , 'prefix_header_search_and_sitemap');
function prefix_header_search_and_sitemap() {
	
	?>
    <form method="get" class="searchform" action="<?php echo home_url('/')?>">
    		<label for="s" class="prefix-hidden">Search this site</label>.txt
			<input type="text" value="Search this website …" name="s" class="s" onfocus="if (this.value == 'Search this website …') {this.value = '';}" onblur="if (this.value == '') {this.value = 'Search this website …';}">
			<input type="submit" class="searchsubmit" value="Search">
	</form>
    
    <?php
	
}
?>

Hello. This search form is HTML5 compliant? Thanks in advance. Joan