title: Curly braces in a YAML file
body: <p>I've found the following <a href="https://github.com/flaiker/ci-cfg-templates/blob/master/travis-ci/libgdx.travis.yml" rel="nofollow noreferrer"><code>.travis.yml</code></a> template.</p>
  
  <p>I've noticed this:</p>
  
  <pre><code>    repo: {GITHUB_USER}/{PROJECT_NAME}
  </code></pre>
  
  <p>Is this a special <code>.yml</code> variable syntax I'm not familiar with? Where can I set these values (<code>GITHUB_USER</code>, <code>PROJECT_NAME</code>)?</p>
  
  <hr>
  
  <p>I know I can use environment variables, like so:</p>
  
  <pre><code>    repo: $GITHUB_USER/$PROJECT_NAME
  </code></pre>
  
  <p>but this syntax looks different.</p>