Act on a field being updated.
This hook is invoked just after field is updated in field_update_field().
$field: The field as it is post-update.
$prior_field: The field as it was pre-update.
$has_data: Whether any data already exists for this field.
Note: this list is generated by pattern matching, so it may include some functions that are not actually implementations of this hook.
function hook_field_update_field($field, $prior_field, $has_data) {
// Reset the static value that keeps track of allowed values for list fields.
drupal_static_reset('list_allowed_values');
}