The validation rules of Codeignniter are as follows:
Required
Matches[field_name]
Min_length[x]
Max_length[x]
Exact_length[x]
Alpha
Alpha_numeric
Alpha_dash
Numeric
Integer
Is_natural
Is_natural_no_zero
Valid_email
Valid_emails
Valid_ip
Valid_base64

Prepping data function helps us to prep the data before use apply rules to it. We can use various prepping function that are:
Xss_clean
Prep_for_form
Prep_url
Strip_image_tags
Encode_php_pags

A delimiter is a sequence of one or more characters used to specify the boundary between separate, independent regions in plain text or other data streams. An example of a delimiter is the comma character, which acts as a field delimiter in a sequence of comma-separated values.

 A callback is simply a function in your controller code that is used in place,or along with, a rule.

Method chaining enables us to vastly simplify the syntax by connecting multiple functions. Example:
$this->db->select(‘name,email’)->from(‘users’)->where(‘id’,5)->limit(10,20);