Callback for `wp_kses_normalize_entities()` regular expression.

This function only accepts valid named entity references, which are finite,
case-sensitive, and highly scrutinized by HTML and XML validators.

function wp_kses_named_entities( $matches ) {
	global $allowedentitynames;

	if ( empty( $matches[1] ) ) {
		return '';
	}

	$i = $matches[1];
	return ( ! in_array( $i, $allowedentitynames, true ) ) ? "&$i;" : "&$i;";
}