question about `while-no-input' in xemacs-base/subr-more.el

;;;###autoload (defmacro while-no-input (&rest body) "Execute BODY only as long as there's no pending input. If input arrives, that ends the execution of BODY, and `while-no-input' returns t. Quitting makes it return nil. If BODY finishes, `while-no-input' returns whatever value BODY produced." (declare (debug t) (indent 0)) (let ((catch-sym (make-symbol "input"))) `(with-local-quit (catch ',catch-sym (let ((throw-on-input ',catch-sym)) (or (input-pending-p) (progn ,＠body)))))))