Wikipedia has a pretty good general explanation of value objects.

• Vo\DateRange for date ranges
• Vo\DateTimeRange for date and time ranges
• Vo\Ip for IPv4 and IPv6 addresses
• Vo\Mac for MAC addresses
• Vo\Money for financial math and formatting using the intl extension

Check the tests to get some ideas on how to use these classes.

http://gws.github.com/php-valueobjects

There is a Dockerfile in the docker directory which can be used to build a version of PHP with the required extensions in order to run tests. If you have a Dockerized composer, you need to pass the --ignore-platform-reqs option to update, install etc. in order to skip the extension checks.