[DateTime](https://developers.google.com/workspace/gmail/markup/reference/types/DateTime) values are expected
to be in the ISO 8601 format, for example `'2013-02-14T13:15:03-08:00'`
(`YYYY-MM-DDTHH:mm:ssZ`).

The following examples show how to generate ISO 8601 datetime strings in several
programming languages.

### Java

    Date date = new Date();
    DateFormat df = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ssZ");
    String dateAsISOString = df.format(date);

### JavaScript

    const d = new Date();
    const date = d.toISOString();

### PHP

    $objDateTime = new DateTime('NOW');
    $isoDate = $objDateTime->format(DateTime::ISO8601);

### Python

    from datetime import datetime
    d = datetime.now()
    date = d.isoformat()

### Ruby

    require 'time'
    d = Time.now
    date = d.utc.iso8601

### Perl

    my $now = time();
    $date = time2isoz($now);

### C++

    time_t now;
    time(&now);
    char buf[sizeof "2011-10-08T07:07:09Z"];
    strftime(buf, sizeof buf, "%FT%TZ", gmtime(&now));