General: Use the semantic <search> element in core search markup.

Wrap the form output of `get_search_form()` (html5 format) and the
`core/search` block in the HTML `<search>` landmark element, and drop
the now-redundant `role="search"` attribute on the inner `<form>`.

The `<search>` element is in Baseline and has an implicit ARIA
landmark role of `search`, providing the same semantics as the
existing `role="search"` attribute via native markup. The XHTML
fallback in `get_search_form()` is left unchanged because XHTML 1.x
does not include the `<search>` element.

For `get_search_form()`, the optional `aria_label` argument is now
applied to the `<search>` landmark element instead of the `<form>`,
since the landmark is what assistive technology exposes.

Props to all who will help review and refine this change.

Author: adamsilverstein

src/wp-includes/blocks/search.php

@@ -189,7 +189,7 @@ function render_block_core_search( $attributes ) {
 	}
 
 	return sprintf(
-		'<form role="search" method="get" action="%1s" %2s %3s>%4s</form>',
+		'<search><form method="get" action="%1s" %2s %3s>%4s</form></search>',
 		esc_url( home_url( '/' ) ),
 		$wrapper_attributes,
 		$form_directives,

src/wp-includes/general-template.php

@@ -322,7 +322,7 @@ function get_search_form( $args = array() ) {
 		}
 
 		if ( 'html5' === $format ) {
-			$form = '<form role="search" ' . $aria_label . 'method="get" class="search-form" action="' . esc_url( home_url( '/' ) ) . '">
+			$form = '<search ' . $aria_label . '><form method="get" class="search-form" action="' . esc_url( home_url( '/' ) ) . '">
 				<label>
 					<span class="screen-reader-text">' .
 					/* translators: Hidden accessibility text. */
@@ -331,7 +331,7 @@ function get_search_form( $args = array() ) {
 					<input type="search" class="search-field" placeholder="' . esc_attr_x( 'Search &hellip;', 'placeholder' ) . '" value="' . get_search_query() . '" name="s" />
 				</label>
 				<input type="submit" class="search-submit" value="' . esc_attr_x( 'Search', 'submit button' ) . '" />
-			</form>';
+			</form></search>';
 		} else {
 			$form = '<form role="search" ' . $aria_label . 'method="get" id="searchform" class="searchform" action="' . esc_url( home_url( '/' ) ) . '">
 				<div>