What is $delta for in Field API hook_field_widget_form? d.o defines it as such:


  $delta The order of this item in the array of subelements (0, 1, 2, etc).


So that you can use it as an index into the $items array, but i can't seem to wrap my head around when the $items array would have more than one element.
See the answer to my question re; delta field in views.  I got an answer for $delta as well.