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:

_attach	When an object is attached to or detached from its parent.
_call	When using an object as if it is a function.
_compare	When comparing an object with another one.
_free	When an object is being freed.
_get	When reading an object as if it is an array.
_init	When the object class is loaded.
_next	When enumerating the object.
_new	When an object is created.
_property	To know if an unknown symbol is a method or a property.
_put	When writing to an object as if it is an array.
_read	When unserializing an object from a stream. Since 3.15
_ready	When an object construction is finished, and an object is ready to be used. Since 3.9
_unknown	When trying to use an unknown object method or property.
_write	When serializing an object to a stream. Since 3.15