Undo History Window

In addition to the Edit|Undo and Edit|Redo commands, the Undo Window allows you to see a timeline of changes you've made and non-destructively revert back to earlier states.

You can assign temporary A/B/C/D presets to items in the undo history for quick comparisons. Simply choose an item in the undo history and click A/B/C/D to assign it to the selected item. The button will turn red to indicate that it is assigned. To change the assignment for a button, hold it until it flashes.

You can also rename items in the undo history by double-clicking them.