Fixing a mistake using the online editor

Problem:

I made a mistake while using the online editor. How do I fix it?

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Solution:

Mistakes happen. Do not worry.
On the second line of the editor's toolbar the first two buttons are the Undoes your last action (Ctrl+Z keyboard shortcut) and Redoes the last action (Ctrl+Y keyboard shortcut) buttons (with two curbed arrows, one pointing left and another one right). Click them to fix your mistakes.
Important: Once you've hit the Submit button, you cannot fix your errors with these two buttons. But you can edit your text using the other tools available.
Also see the visual tutorial How to: Use the online editor- Basic operations, text formatting.