title: Does circleci checkout pull the latest code from master or the code for the specific commit
body: <p>Hello stackoverflow/circleci gods.</p>
  
  <p>I have been using circleCI for a while now and I have a question about the 'checkout' step which I will do my best to explain. This is a snippet from my circleCI config file (I have a job 'a-job' whose first step is checkout):</p>
  
  <pre><code>a-job:
    docker:
      - image: docker-image-here
    steps:
      - checkout
      ...
  </code></pre>
  
  <p>My question is, does the circleci step 'checkout' pull the latest code from master or the code for the specific commit.</p>
  
  <p>i.e. does checkout simply git clone master:latest or does it git clone SPECIFIC COMMIT HERE</p>