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

_new	When an object is created.
_init	When the object class is loaded.
_get _put	When using an object as if it is an array.
_next	When enumerating the object.
_call	When using an object as if it is a function.
_unknown	When trying to use an unknown object method or property.
_compare	When comparing an object with another one.