Hello Matthias,

Thank you for trying EmEditor Professional!

I reproduced your issue, and the problem was the Line Comment (--) has more priority than multiline comment (--[[...]]). If you remove the string (--) from Line Comment text box in the Highlight (2) tab of configuration properties, it works. I am not sure if I can correct this behavior at this moment.

If you want both types of comments highlighted, instead of specifying -- in the Highlight (2) tab, you can add -- in the Highlight (1) tab, check "Highlight Right Side", and select your favorite color (1 - 10). You will also need to remove the already defined keyword (-) from the list.

I hope this helps.
Please don't hesitate to ask me if you have further questions.
Thank you,

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Yutaka Emura
Developer of EmEditor
http://www.emeditor.com/