src/Common/Internal/Utilities.php
public static function isoDate($timestamp = null)
    {
        $tz = date_default_timezone_get();
        date_default_timezone_set('UTC');

        if (is_null($timestamp)) {
            $timestamp = time();
        }

        $returnValue = str_replace(
            '+00:00', '.0000000Z', date('c', $timestamp)
        );
        date_default_timezone_set($tz);

        return $returnValue;
    }
public static function isoDate($timestamp = null)
    {
        $tz = date_default_timezone_get();
        date_default_timezone_set('UTC');

        if (is_null($timestamp)) {
            $timestamp = time();
        }

        $returnValue = str_replace(
            '+00:00', '.0000000Z', date('c', $timestamp)
        );
        date_default_timezone_set($tz);

        return $returnValue;
    }
public static function isoDate ( $ timestamp = null ) { $ tz = date_default_timezone_get ( ) ; date_default_timezone_set ( 'UTC' ) ; if ( is_null ( $ timestamp ) ) { $ timestamp = time ( ) ; } $ returnValue = str_replace ( '+00:00' , '.0000000Z' , date ( 'c' , $ timestamp ) ) ; date_default_timezone_set ( $ tz ) ; return $ returnValue ; }
Generate ISO 8601 compliant date string in UTC time zone.

@param int $timestamp The unix timestamp to convert
(for DateTime check date_timestamp_get)

@static

@return string
Generate ISO 8601 compliant date string in UTC time zone .