one of the documented procedures in this installation of the ACS
download_date_form_check   form   date_name
What it does:
checks that date_name is a valid date. Returns a list of date_name exception_count, exception_text. Sets date_name to a YYYY-MM-DD format.
Defined in: /web/philip/tcl/download-defs.tcl

Source code:

    set encoded_date [ns_urlencode $date_name]

    ns_set update $form "ColValue.$" [string trimleft [ns_set get $form ColValue.$] "0"]

    # check that either all elements are blank or date is formated 
    # correctly for ns_dbformvalue
    if { [empty_string_p [ns_set get $form ColValue.$]] && 
    [empty_string_p [ns_set get $form ColValue.$encoded_date.year]] && 
    [empty_string_p [ns_set get $form ColValue.$encoded_date.month]] } {
	return [list "" 0 ""]
    } elseif { [catch  { ns_dbformvalue $form $date_name date $date_name} errmsg ] } {
	return [list "" 1 "<li>The date or time was specified in the wrong format.  The date should be in the format Month DD YYYY.\n"]
    } elseif { ![empty_string_p [ns_set get $form ColValue.$encoded_date.year]] && [string length [ns_set get $form ColValue.$encoded_date.year]] != 4 } {
	return [list "" 1 "<li>The year needs to contain 4 digits.\n"]
    return [list [set $date_name] 0 ""]