Access Control confusion

[Chang Min Jeon]

[Note: parts of this message were removed to make it a legal post.]

I read Ruby User's Guide <http://www.rubyist.net/~slagell/ruby/>
created by Yukihiro Matsumoto

http://www.rubyist.net/~slagell/ruby/accesscontrol.html

and i have a question about access control.
Access Control section explain method following code.

* def square(n)*

|* n * n*
|* end*

Object class has square method.

But it is not allowed access of square method following document.

We are not allowed to explicitly apply the method to an object:

ruby>* "fish".square(5)*
*ERR: (eval):1: private method `square' called for "fish":String*

But it is operated when i write code above in ruby 1.8.7

What is the matter ?
wrong document ?