WordPress at a glance
filter is not described

search_form_format filter-hook . WP 3.6.0

Filters the HTML format of the search form.

Usage

add_filter( 'search_form_format', 'filter_function_name_7679' );
function filter_function_name_7679( $format ){
	// filter...

	return $format;
}
$format(string)
The type of markup to use in the search form. Accepts 'html5', 'xhtml'.

Where the hook is called

get_search_form()
wp-includes/general-template.php 201
$format = apply_filters( 'search_form_format', $format );

Where the hook is used (in WP core)

Does not used.