While "tie" in perldoc allows tying to an arbitrary object, the class in
question must support this in it's implementation of TIEHASH, TIEARRAY or
whatever.

This class provides a very tie constructor that simply returns the object it
was given as it's first argument.

This way side effects of calling $object->TIEHASH are avoided.

This is used in Data::Visitor in order to tie a variable to an already existing
object. This is also useful for cloning, when you want to clone the internal
state object instead of going through the tie interface for that variable.