Using ArcSDE with a relational database, it is possible to set up versioning. Is this available in ArcGIS Online, aka ArcGIS.com?
When working with a feature layer in ArcGIS Online, there is the option to allow editing, and to ensure only the feature's creator can make changes. But this isn't the same thing as fully-fledged versioning, allowing the ability to merge conflicts, etc.
Is versioning supported using ArcGIS Online?