Handling of typos in form validation rules

[eluser]voidstar[/eluser]
Hello,

I just completed my first CI project, and I'm very pleased with the result. CI is great! Its structure and built-in facilities were very helpful!

One of the facilities that I used was Form Validation, and although it generally worked very well, I found one anomaly: invalid rules are ignored. For example in the following rule fragment "exact_length" is misspelled.

array(
'field' => 'yyyy',
'label' => 'Year',
'rules' => 'trim|required|exact_lngth[4]|is_natural_no_zero|callback__yyyy_check'
)

Form validation apparently ignores rules that it doesn't recognize. I don't know whether this is a feature or a bug, but if it is a feature, it should be documented.

I found post about a closely related problem, i.e. a misspelled callback function, here.
http://ellislab.com/forums/viewthread/92501/