下列常量由此扩展定义，且仅在此扩展编译入 PHP 或在运行时动态载入时可用。
YAF_VERSION
(string)
YAF_ENVIRON
(string)
YAF_ERR_STARTUP_FAILED
(integer)
YAF_ERR_ROUTE_FAILED
(integer)
YAF_ERR_DISPATCH_FAILED
(integer)
YAF_ERR_AUTOLOAD_FAILED
(integer)
YAF_ERR_NOTFOUND_MODULE
(integer)
YAF_ERR_NOTFOUND_CONTROLLER
(integer)
YAF_ERR_NOTFOUND_ACTION
(integer)
YAF_ERR_NOTFOUND_VIEW
(integer)
YAF_ERR_CALL_FAILED
(integer)
YAF_ERR_TYPE_ERROR
(integer)