Depending on the kind of change it sometimes makes sense to incorporate our changes in the other version or vice versa. Users should be able to select the most sensible starting point.
When the merge screen is opened, the text editor should not yet display any text. Instead, it should have grey bars indicating text and a box that allows users to select their base version for the merge. Clicking "OK" will then fill the text editor with the chosen text.
Please also change the explanatory text of the editor column as described in the mock for js users.
For non-js users, the text stays as it currently is.