WordPress at a glance
filter is not described

extra_theme_headers filter-hook . WP 1.0

Usage

add_filter( 'extra_theme_headers', 'filter_function_name_4478' );
function filter_function_name_4478( $array ){
	// filter...

	return $array;
}
$array
-

Where the hook is called

get_theme_data()
extra_theme_headers
wp-includes/deprecated.php 3077
foreach ( apply_filters( 'extra_theme_headers', array() ) as $extra_header ) {

Where the hook is used (in WP core)

Does not used.