If you have marked one or more lines at one or both sides of the difference display then this command marks the text lines as ‘deleted’. The “Undo” menu function reverses this action. The “Save Modifications” command then actually deletes the lines in the corresponding text file.
Clear is available in text file comparisons only, and only where the side may
be written — Merging Changes lists the cases in
which the command is greyed out, from archive entries to a side locked with
/read-only.