По поводу закрытия предпросмотра:
Jay Salvat:
You can close the preview by clicking the Preview button with Alt Key
pressed.
I have to add a more convenient 'close' button, but not so much time
to work on markItUp! for the moment.
You can also deactivate the autorefreshed preview.
По поводу подсветки ббкода:
Jay Salvat:
The Code Highlight is the most asked feature.
markItUp! enhances native textarea, and unfortunatly CSS doesn't allow
multiple colors in one textarea.
So it's impossible to implement the way markItUp! works. Really sorry