src/Aspose/Storage/ObjectSerializer.php
public static function toString($value)
    {
        if (date(\DATE_ATOM, preg_match("/^[1-9][0-9]*$/", $value)[0]) instanceof \DateTime) { // datetime in ISO8601 format
            $datetime = preg_match("/^[1-9][0-9]*$/", $value)[0];
            return date(\DATE_ATOM, $datetime);
        } else {
            return $value;
        }
    }
public static function toString($value)
    {
        if (date(\DATE_ATOM, preg_match("/^[1-9][0-9]*$/", $value)[0]) instanceof \DateTime) { // datetime in ISO8601 format
            $datetime = preg_match("/^[1-9][0-9]*$/", $value)[0];
            return date(\DATE_ATOM, $datetime);
        } else {
            return $value;
        }
    }
/*
Take value and turn it into a string suitable for inclusion in
the parameter. If it's a string, pass through unchanged
If it's a datetime object, format it in ISO8601

@param string|\DateTime $value the value of the parameter

@return string the header string