How does Codeigniter handle escaping output?

I am using CodeIgniter.

Recently, I read a PHP book and saw some functions to escape output to server to database using

*_escape_string()

and from server to browser using:

htmlentities()
htmlspecialchars()

In my Codeigniter application, how are these functions handled? Is it internally handled by the framework, or do I have to manually handle it?

In Ccodeigniter form validation I have seen xss_clean

$this->form_validation->set_rules('password', 'Password', 'required|xss_clean|min_length[6]|matches[confirmpassword]' );

Is xss_clean for preventing cross site scripting, or does it deal with the above I have mentioned?