Google Drive allows version control, where multiple copies of the same file can be stored and retrieved. This functionality is also available in the draw.io interface.
The user can create a new file revision at any time by selecting File -> Create revision. New revisions of files are also created on closing a diagram and every 30 minutes while working on a diagram.
The number of revisions for any given file is capped at 100. After that, each new revision causes the oldest revision to be deleted.
It is possible to view the revision history for a file. Selecting File -> Revision history brings up a new window showing all revisions for the currently open file.
When the window first opens, the current revision is highlighted in the list of available revisions, located in the top left hand corner. By left-clicking on any revision in the list, you cause the diagram associated with that revision to appear in the main view. This view is read-only, although there are magnification controls located below the bottom left hand corner of the diagram. In addition, by left or right clicking on the diagram and dragging, it is possible to scroll around the diagram at different magnifications.
Having examined different revisions of the diagram, you have a number of options available to you, located in the bottom right hand corner of the window:
Show will open a new tab containing a larger read-only view of the selected revision. Magnification controls are once again avaialble in the top-left of the diagram.
Selecting any revision from the list (apart from the current one) and then Restore will open a prompt window
Choosing OK will close the window and load that revision of the diagram into the editor. This old revision will then become the new current revision.
Close will simply close the window and return you to the editor.