In this chapter you learned that you can indeed turn back time, at least as far as Photoshop is concerned. You learned about using the Undo and Revert commands, and how to use the History panel and History states to step back to previous stages in your document's evolution. You learned how to paint back in parts of a History state using the History Brush, effectively bringing bits of the past into the present. You saw how you could use snapshots to save History states or create new documents from them.
You also learned about non-destructive image editing and the tools that are commonly used in a non-destructive workflow, including adjustment layers, layer masks, layer comps, and Smart Objects.