If you want a little more workspace, the ribbon can be hidden with a single click on the currently active tab or by clicking a small arrow appearing at the ribbon's far right side. Microsoft has also added a new "Help Improve Office?" button to the ribbon, which you can use to send feedback. According to the rep I spoke with, this isn't a beta-only feature that will disappear once the product ships. It's designed to let you tell Microsoft about the things you do or don't love about a particular product.
True story: The Microsoft rep I spoke with said that this feature is no joke. He acknowledged that there is a public perception that any feedback of this sort gets sent directly to the bit bucket, but he assured me that he sees "telemetry reports" from these submissions on a daily basis. The aim of this feature is to help eliminate that public perception by proactively responding to reported issues.
Office now supports Yosemite's native full-screen mode, but does not support Yosemite's native auto-save features nor does it support renaming, moving, tagging, or locking documents using the document title bar. And it should be noted that it's unlikely you'll see support for these features in any future versions of Office, as, according to Microsoft, Yosemite's autosave feature and OneDrive don't play well together. The one notable autosave exception is (pun intended) OneNote, which has had its own version of autosave and synchronization since it was first released.
Word and PowerPoint share two new collaboration features: co-authoring and threaded comments. Co-authoring allows several people to work on the same document at the same time. The Microsoft rep wouldn't commit to a specific number of total editors that could simultaneously make changes to a document, but did state that they'd seen it handle at least 10 collaborators at once. (A number that's quite a bit north of what I'd hope to see working on any one document.) While editing, you can see who is working alongside you and also see the changes those users are making in real time.
To handle synchronization and change commitment, Microsoft uses a technology they call cobalt syncing. Cobalt is able to determine which changes users have made, and in the event that two users edit the same information at the same time, marks those changes and conflicts for human intervention.
Threaded comments let editors interact within document comments, in much the same way as threaded comments work on websites, but hopefully with far less snark.
Word also includes a new document navigation pane that tracks your location within a document and makes it easy to move your way through a document. A new style pane allows you to make quick changes to styles being used in your documents.
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