title: What do the &,<<, * mean in this database.yml file?
body: <p>Up until now I have only used <code>database.yml</code> with each parameter called out explicitly, in the file below it uses some characters I do not understand. What does each line and symbol(<code>&amp;</code>, <code>*</code>, <code>&lt;&lt;</code>) mean? How do I read this file?</p>
  <pre><code>development: &amp;default
    adapter: postgresql
    database: dev_development
  
  test: &amp;test
    &lt;&lt;: *default
    database: test_test
  
  
  cucumber:
    &lt;&lt;: *test
  
  production:
    &lt;&lt;: *default
    database: test_production
  </code></pre>