Every save is kept as a revision, so a bad edit can always be undone. Open a page's History tab to see who changed what, when, and by how much.
To compare two versions:
- On the History tab, each row has two radio buttons. Pick one in the first position on one row and one in the second position on another.
- Click Compare selected revisions.
- Removed lines appear in red with a minus sign and added lines in green with a plus sign.
To undo a change, click Restore beside the version you want back. This adds a new revision with the old text, so nothing in the history is lost.
If someone else saves a page while you are editing it, your save is stopped so neither of you overwrites the other. You will see a warning and a list of their changes, and your text stays in the editor. Work their changes into yours if needed, then save again. Saving at that point replaces their version with what is in your editor.