function rewrite_rules() {
add_rewrite_tag( '%userid%', '([^&]+)', 'userid=' );
add_rewrite_tag( '%block%', '([^&]+)', 'block=' );
add_rewrite_rule( '^user/([^/]*)/?', 'index.php?page_id=17&userid=$matches[1]&block=$matches[2]', 'top' );
add_filter( 'query_vars', function( $vars ) {
$vars[] = 'userid';
$vars[] = 'block';
return $vars;
} );
}
add_action( 'init', 'rewrite_rules' );