title: List of all the App Engine images service get_serving_url() URI options
body: <p>In response to <a href="https://stackoverflow.com/questions/22293229/google-app-engine-busting-serving-url-cache">another question</a>, a commenter mentioned an undocumented URI option I was not aware of to flip images horizontally/vertically with the App Engine images service.</p>
  
  <p><a href="https://developers.google.com/appengine/docs/java/images/#using_if_lang_is_java_getservingurl_endif_if_lang_is_python_get_serving_url_endif" rel="noreferrer">The documentation</a> mentions a few basic options:</p>
  
  <ul>
  <li>=s0 &mdash; fullsize</li>
  <li>=s640 &mdash; longest edge 640px long</li>
  <li>=s640-c &mdash; 640px square</li>
  </ul>
  
  <p>Would be nice to generate a comprehensive list of options, or if someone could provide any more options they know about here to serve as de facto documentation.</p>