18. The computer-readable storage device of claim 17 , wherein the first computing device is further caused to display the first annotation when the first user moves a cursor to the first unit of data.
17. A computer-readable storage device comprising instructions that, when executed by a first computing device, cause the first computing device to: allow a first unit of data of a document to be edited by a first user; when the first unit of data is edited, provide a first annotation displayed on the document at the first computing device indicating that the document is being edited by the first user; send a first update from the first computing device to a second computing device indicating that the first unit of data of the document is being edited; receive a second update from the second computing device at the first computing device indicating that a second user is editing a second unit of data of the document; provide a second annotation displayed on the document indicating that the second unit of data is being edited by the second user, without displaying the content updates to the second unit of data; receive an indication from the first user to display the content updates into the document from the second computing device; and update, by the first computing device, the document to display the content updates.