&reftitle.runtime; &extension.runtime; Name Default Changeable unserialize_callback_func "" PHP_INI_ALL For further details and definition of the PHP_INI_* constants see ini_set. &ini.descriptions.title; unserialize_callback_func string The unserialize callback function will called (with the undefined class' name as parameter), if the unserializer finds an undefined class which should be instanciated. A warning appears if the specified function is not defined, or if the function doesn't include/implement the missing class. So only set this entry, if you really want to implement such a callback-function. See also unserialize.