{
if (is_null($value)) {
return true;
}
if ( ! preg_match('/^\s*(\d{2}):(\d{2})(:(\d{2}))?(\.(\d{1,6}))?([+-]\d{1,2}(:(\d{2}))?)?\s*$/', $value, $matches)) {
return false;
}
$hh = (isset($matches[1])) ? intval($matches[1]) : 0;
$mm = (isset($matches[2])) ? intval($matches[2]) : 0;
$ss = (isset($matches[4])) ? intval($matches[4]) : 0;
$ms = (isset($matches[6])) ? intval($matches[6]) : 0;
$tz_hh = (isset($matches[7])) ? intval($matches[7]) : 0;
$tz_mm = (isset($matches[9])) ? intval($matches[9]) : 0;
return ($hh >= 0 && $hh <= 23) &&
($mm >= 0 && $mm <= 59) &&
($ss >= 0 && $ss <= 59) &&
($tz_hh >= -13 && $tz_hh <= 14) &&
($tz_mm >= 0 && $tz_mm <= 59) ;
}