anchor.diff:  <table>
   <tbody>
     <tr><th><code>author</code></th><td>A hash with a <code>"name"</code> and <code>"email"</code> key to show who created this build.<br><em>Default value: the user making the API request</em>.</td></tr>
  +  <tr><th><code>clean_checkout</code></th><td>Force the agent to remove any existing build directory and perform a fresh checkout.<br><em>Default value:</em> <code>false</code>.</td></tr>
     <tr><th><code>env</code></th><td>Environment variables to be made available to the build.<br><em>Default value:</em> <code>{}</code>.</td></tr>
  +  <tr><th><code>ignore_pipeline_branch_filters</code></th><td>Run the build regardless of the pipeline’s branch filtering rules. Step branch filtering rules will still apply.<br><em>Default value:</em> <code>false</code>.</td></tr>
     <tr><th><code>meta_data</code></th><td>A hash of meta-data to make available to the build.<br><em>Default value:</em> <code>{}</code>.</td></tr>
  -  <tr><th><code>ignore_pipeline_branch_filters</code></th><td>Run the build regardless of the pipeline’s branch filtering rules. Step branch filtering rules will still apply.<br><em>Default value:</em> <code>false</code>.</td></tr>
  -  <tr><th><code>clean_checkout</code></th><td>Force the agent to remove any existing build directory and perform a fresh checkout.<br><em>Default value:</em> <code>false</code>.</td></tr>
  +  <tr><th><code>pull_request_base_branch</code></th><td>For a pull request build, the base branch of the pull request.<br><em>Example:</em> <code>"master"</code></td></tr>
  +  <tr><th><code>pull_request_id</code></th><td>For a pull request build, the pull request number.<br><em>Example:</em> <code>42</code></td></tr>
  +  <tr><th><code>pull_request_repository</code></th><td>For a pull request build, the git repository of the pull request.<br><em>Example:</em> <code>"git://github.com/my-org/my-repo.git"</code></td></tr>
     </tbody>
   </table>
   
  
positive.code:   "started_at": "2015-05-09T21:05:59.874Z",
    "finished_at": "2015-05-09T21:05:59.874Z",
    "meta_data": { },
    "pipeline": {
      "id": "849411f9-9e6d-4739-a0d8-e247088e9b52",
      "url": "https://api.buildkite.com/v2/organizations/my-great-org/pipelines/my-pipeline",
  
negative.code:   "started_at": "2015-05-09T21:05:59.874Z",
    "finished_at": "2015-05-09T21:05:59.874Z",
    "meta_data": { },
    "pull_request": { },
    "pipeline": {
      "id": "849411f9-9e6d-4739-a0d8-e247088e9b52",
      "url": "https://api.buildkite.com/v2/organizations/my-great-org/pipelines/my-pipeline",
  