Undo and Redo Changes

This chapter creates one semantic typing unit, reverses and reapplies it, creates a retained alternate future, and identifies the current interactive boundary for branch and selective history operations.

Before You Begin

If you enter this chapter directly, first complete Prepare the User Guide Exercises.

Complete Transfer Text. Reopen the unchanged kit-supplied editing-practice file if necessary:

odra ~/odra-guide/work/dirs/notes/editing-practice.txt

Point begins before Editing Practice.

Create One Typing Unit

Type ax, press Backspace, then type 界. The first line becomes:

a界Editing Practice

These input events form one semantic typing unit. The local Backspace remains in the unit because it corrects text inserted by that same compatible typing sequence.

Cursor movement, a separate semantic command, or an incompatible edit ends the current typing unit.

Undo the Complete Unit

Press C-/. The complete a界 insertion disappears in one operation, and point returns to the position recorded before the unit.

C-_ and C-x u invoke the same undo command. Undo at the initial history state is a checked no-op: it does not change text or create another history entry.

Redo Through Command Navigation

The factory profile has no direct redo binding. Press M-x, enter redo, and press Enter. The complete typing unit returns, including its final cursor context.

Undo and redo publish fresh revisions. Returning to identical text does not reuse an older revision or make stale positions current again.

Record a Keyboard Macro

Press C-x ( to start recording, perform a short sequence, and press C-x ) to finish. Press C-x e to replay the last macro. F4 finishes an active recording or replays the last completed macro. Repetition is bounded, and a failed step stops replay without executing later steps.

Create an Alternate Future

Press C-/ to return to the file's initial text. Type note instead of redoing a界. This creates a new child from the same earlier state; it does not erase the retained a界 history branch.

Run redo through M-x while positioned at the new leaf. Nothing changes because that active node has no preferred child. Press C-/ to undo note , then run redo again. The preferred note unit returns.

Odra currently exposes ordinary undo and preferred-child redo through the interactive command surface. Retained alternate-child selection and selective undo are checked native capabilities without an ordinary interactive selector, so this User Guide does not invent keys or ask you to manipulate internal node identities. Their exact contracts remain documented in the history reference.

Restore Editing Context

History records the initiating cursor context around a logical edit. When an edit begins with point, mark, and an active region, undo restores their before state and redo restores their after state. Other views of the same buffer keep their own stored points and viewports.

An explicitly linked multibuffer edit is also retained as one logical unit and cannot be partially traversed. User-facing workflows that create such edits, including editable result application, teach the visible behavior where those workflows are introduced.

Recover from History Surprises

• Undo at the root and redo without a preferred child are safe no-ops.
• If one undo removes more characters than expected, the edits belonged to one semantic typing unit; movement or another semantic command ends future groups.
• If editing after undo changes what ordinary redo reapplies, you created a new preferred branch. The older branch remains retained but has no current interactive selector.
• Save only after the buffer shows the intended state. Exit cancellation still protects any modified result.

Verify the Result

You have completed this chapter when one undo removes the complete corrected a界 unit, M-x redo restores it, editing after undo creates a new preferred future, and undo plus redo traverses that new note unit as one operation.

Undo note before leaving the file, then continue with Save and Revisit Editor State.

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