I tried some other plugins based on shortcodes, but they went too far and didn't format linebreaks the way I wanted. Plus, they prevented other shortcodes from being processed.
This plugin was easy to install and required no changes to my code. All I had to do was use the Fix It Tools like the instructions said. A few mouse clicks later, everything looked perfect.
Now I can switch back and forth between the Visual and HTML tabs without losing any formatting. HTML that used to be stripped out is now preserved, and I can format everything exactly the way I want.
Marcus, thank you so much for this great plugin! I couldn't ask for more.