If you have copied lines from one side to the other side, pasted lines from the clipboard or marked one or more lines as ‘deleted’, then Undo restores the original text lines.
Diffoniq keeps a history of your edits (per file pair): each
Undo (Ctrl+Z) takes back one more edit, and
Redo (Ctrl+Y or Ctrl+Shift+Z) applies
the undone edits again, most recently undone first. Making a new edit after an
Undo discards the remaining Redo steps. When there is nothing left to undo or
redo, the corresponding menu item is greyed. Reloading or re-comparing the
files clears the history. Wherever no edits are possible — read-only
views, files inside an archive, the read-only file attribute, or a side locked
with /read-only on the
command line, see
Merging Changes — Undo and Redo are always
greyed.