validation reference in codeigniter

[eluser]mistress_shiira[/eluser]
good day!ive been trying to make a validation form...i have read the tutorial on the validation class.but there is something that i want to learn more.this is regarding setting the rules for validation.
example i have this:
$rules['email'] = 'required|trim|valid_email';

there was a note that if i wanted to know more about validation rules i will just look up validation reference..but for the life of me i dont know where it is.
can anyone send me a link to it?i want to know the available rules that i can use.
thanks