Add any special tokens this field might use for itself.
This method is intended to be overridden by items that generate fields as a list. For example, the field that displays all terms on a node might have tokens for the tid and the term.
By convention, tokens should follow the format of [token-subtoken] where token is the field ID and subtoken is the field. If the field ID is terms, then the tokens might be [terms-tid] and [terms-name].
function add_self_tokens(&$tokens, $item) {
}