How do etherpad & Google Docs do ChangeSets

I'm curious to learn how Etherpad and Google Docs automatically save data. When you're writing a text document the products send only the changes to the server. Any idea how this technology works and where I ca开发者_运维问答n go to learn more about the end-2-end?

Thanks

Etherpad and Google Wave use Operational Transforms. Here's an article about their use in Google Wave.

John McLear here from the Etherpad foundation.

Here is a document discussing Etherpad handles changesets.