title: Colon in the front: YAML syntax
body: <p>I'm currently using Sidekiq in a project and I have the following YAML config file:</p>
  
  <pre><code>:concurrency: 5
  :pidfile: /tmp/pids/sidekiq.pid
  :logfile: log/sidekiq.log
  staging:
    :concurrency: 10
  production:
    :concurrency: 20
  queues:
    - default
  </code></pre>
  
  <p>I haven't seen having a colon in front of a key before but omitting that colon produces interesting results. In the case of the <code>:pidfile:</code> for example, with the colon in front it creates/overrides the destination file where is without it, it uses the one already there and does not write to it.</p>
  
  <p>Is this documented somewhere or is this simply how Sidekiq expects certain keys?</p>