title: How to check the docker-compose file version?
body: <p>I would like to make sure that I'm using version 3 of the compose file format. However, on <a href="https://docs.docker.com/compose/compose-file/" rel="noreferrer">https://docs.docker.com/compose/compose-file/</a> I was not able to find out how to do this.</p>
  
  <p>My Docker version is <code>17.04.0-ce, build 4845c56</code>, and my Docker-Compose version is <code>docker-compose version 1.9.0, build 2585387</code>. I'm not sure since when version 3 of the compose file format was introduced, however. How can I find this out?</p>