WordPress at a glance
filter is not described

extra_(context)_headers filter-hook . WP 2.9.0

Filters extra file headers by context.

The dynamic portion of the hook name, $context, refers to the context where extra headers might be loaded.

Usage

add_filter( 'extra_(context)_headers', 'filter_function_name_2041' );
function filter_function_name_2041( $extra_context_headers ){
	// filter...

	return $extra_context_headers;
}
$extra_context_headers(array)
Empty array by default.

Where the hook is called

get_file_data()
extra_(context)_headers
wp-includes/functions.php 4912
if ( $context && $extra_headers = apply_filters( "extra_{$context}_headers", array() ) ) {

Where the hook is used (in WP core)

Does not used.