//FIXME: need better wording here. users should be made aware that this is for advanced use. It might be nice to provide a list of the more common date format characters. It may be helpful to know that it overrides settings such as the one above show_full_date, and only if kept empty will the other date formats apply. For non-English users, it also may be helpful to know that the format is still passed through our own date_intl() function which translates things like the day of the week, month names and abbreviations, etc.
'trailing_text' => ' ' . _("(Uses format of PHP date() function)"),