I'm investigating Google Drive's real-time API. In the [QuickStart Tutorial](https://developers.google.com/drive/realtime/realtime-quickstart) the JavaScript library loaded is <https://apis.google.com/js/api.js>. The Drive documentation [describes](https://developers.google.com/drive/realtime/application#step_2_load_the_realtime_library) this library as the Google JavaScript API loader. This library seems to load the appropriate libraries for the services we need to interact with.

But when looking at [QuickStart Tutorial](https://developers.google.com/drive/web/quickstart/quickstart-js) for Google Drive (non realtime) it seems to load <https://apis.google.com/js/client.js> which I believe is the library documented [here](https://code.google.com/p/google-api-javascript-client/).

My question is what is the difference between api.js and client.js. They seem to have similar purpose although don't work in the same way. Is api.js for certain Google API's while client.js is for others? Is api.js documented somewhere like client.js is?