These are the defined callback functions which CCK will call. They are similar to Drupal's core hooks, but not part of that set. They follow the same naming convention, that is, if your module is named foo and defines a CCK field, then the hook_field function would be named foo_field().
Required CCK hooks for CCK fields
- hook_field_info - To define new field type(s) in your module, use hook_field_info to tell CCK about those types.
For example, number.module defines
number_float. And text.module simply defines