Version history keeps snapshots of a piece so you can experiment freely.
Save a version
In the editor, choose History in the side panel. On a phone, tap the panel icon at the top (just left of the ⋯ menu) first.
Under Save a version, add a note if you like, such as "Before tightening".
Tap Save.
Restore a version
In History, tap a version to preview it.
Tap Restore this version, then tap Restore to confirm.
You can also tap Restore next to a version in the list. On a computer it appears when you point at the version.
Your current text is saved as a version first, so you can always switch back.
Undo
For small changes, use the undo arrow at the left of the toolbar, or press Ctrl+Z (⌘+Z on Mac).