If I properly recall, I've splitted some huge and hard to use and understand method to separated callbacks for every field type right after 1.4.2 release. Well... it doesn't matter when, but yes - now there is a default QFfield callback for every field type in Utils_RecordBrowserCommon.
If you would like to see this in code, just open modules/Utils/RecordBrowser/RecordBrowserCommon_0.php on lines 2565.
There is a method to obtain default QFfield callback for specified type followed by all default QFfield callbacks.
Those types have their default QFfield callbacks:
$types = array('hidden', 'checkbox', 'calculated', 'integer', 'float',
'currency', 'text', 'long text', 'date', 'timestamp', 'time',
'commondata', 'select', 'multiselect', 'autonumber');
If you want to do something using Custom QFfield callback, but preserve default behavior of field then define custom method and call default callback like in code I've typed for you.
I know that EPESI is lacking of documentation, but we will try to change this.
Regards,
Adam