Type text mirrored horizontally
A certain version of notepad++ (6.5.5 as reported here and here) had a weird bug; when changing text direction to right-to-left, the text would be mirrored horizontally. I have always wanted such a feature. The nice thing is that it was consistent and worked even for right-to-left languages like Arabic and Hebrew.
How did that happen and how to re-implement it as a plugin?