+if ( isset( $_SERVER['HTTP_IF_NONE_MATCH'] ) && stripslashes( $_SERVER['HTTP_IF_NONE_MATCH'] ) === $wp_version ) {
+ $protocol = $_SERVER['SERVER_PROTOCOL'];
+ if ( ! in_array( $protocol, array( 'HTTP/1.1', 'HTTP/2', 'HTTP/2.0' ) ) ) {
+ $protocol = 'HTTP/1.0';
+ }
+ header( "$protocol 304 Not Modified" );
+ exit();
+}
+