For information on how variables behave, see the Variables entry in the Language Reference section of the manual.
php.ini中的設定會影響這些函數的行為。
For further details and definition of the PHP_INI_* constants see ini_set().
Here is a short explanation of the configuration directives.
The unserialize callback function will called (with the undefind 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().