Anyway, thank you for the help.

But I also found out, this happens only at Obsidian. Not the other themes.

Hmm, maybe use the Compare plugin to look at your Obsidian.xml theme vs the master copy of Obsidian.xml, and see whether any of the differences jump out as “this may break things”.

But I also found out, this happens only at Obsidian. Not the other themes.
I customized the settings of Obsidian before, maybe that’s the problem.

@PeterJones
Strange, with clua it’s working. Not so with .con file.
Maybe because I used it as user extension for other themes before?

Doubtful.

I tried some experiments. The first time I tried using clua con mdl module as my user-extensions, I thought I replicated your results, and when I opened blah.con, it seemed to mark it as text.

I was starting to think that con was somehow getting confused with CON, the DOS console pseudo-file. I know that in other circumstances, the “user extension” also applies if it’s the exact name of the file, and I thought maybe the DOS pseudo-files would create extensions that didn’t work. So I changed to clua con prn nul mdl module, and opened some files with those extensions: now all of them interpreted as Lua, even the .con file.

I went to just con as the user-extension list, and opening other.con worked and was associated as Lua.

I tried going back to clua con mdl module, and now that’s working – every .con file I open, or when I create a new file and save-as anything.con, it works for me. I can exit and restart Notepad++, and that mapping is still there.

You might try clearing the user extensions for Lua, setting it only to con, exiting Notepad++ and coming back in, and see if it works.

If not, please share your ? menu Debug Info (you can copy/paste from that dialog into your reply)

Maybe because I used it as user extension for other themes before?

The user ext. field is apparently saved per-theme, so when you change from one theme to another, the changes you made in the first theme (including the user extension list) don’t apply to any other theme.

Thus, the sequence I had to go through to make it work for a new theme:

1. Select theme (Obsidian)
2. Save and close Style Configurator
   (you have to save&close here, because right now, the user extension box doesn’t exist)
3. Style Configurator > Lua
4. add your custom extension (my experiment used clua, which was short for “custom lua”)
5. save and close Style Configurator
6. Now if you open a standard blah.lua or a custom blah.clua, both will use the Lua syntax highlighting.