Special methods are methods declared in classes, whose name begins with an underscore character, and that are called by the interpreter in some special situations.

They are eight different special methods, and they are all optional.

_init	Class initialization.
_exit	Class clean-up.
_new	Object instanciation.
_free	Object release.
_next	Object or class enumeration.
_get	Array read operator.
_put	Array write operator.
_call	Using the object or the class as a method.
_unknown	Calling an unknown method or property.