Chat in Docs and Slides has a new look similar to what you’re used to in Gmail. You can now start a group chat with just one click. Simply select the new chat button at the top right and a chat box will appear, making it easy for you to quickly message everyone who is in the file. Additionally, if collaborators or viewers have an active Google+ profile, you will see their profile picture on top instead of just their name. This feature will be available in Sheets soon.
Note: Disabling chat in the Admin panel will disable it in Docs.
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