I could not find it anywhere -- neither in the help, nor in the forum, nor in google search (site:...); and i could not understand, while tried to use it.
It's for the layout of the tag-panel and it is mentioned in the help there.
That sounds really useful. Gonna give that a go for sure.
Can it be used to separate headings in the main window?
Really. Thank you for the help.
I used it earlier, but have already forgotten about. We can see it everywhere, for example in the action groups, this was confusing for me.
Really? In which action-type?
I don't see this here. Maybe you have added it yourself?
In Format value action, for example: Action groups >> Create new >> Create new action >> Format string >> arrow at right from "Format string" >> there seems _separator:
But: now i did a new, clean (portable) installation, too. And there is no _separator... It does not seem, likely that I typed it by hand anywhen.
The last fresh install i did 3 years ago, on my new laptop; since then i did just updates.
You can find out if this is a user-defined field or a standard one if you reset the list with the functions of the right-arrow-button next to the field selector.
(On my PC I did not have the field name _SEPARATOR and I did not get it after the reset).
Probably you are right, now i try it. Sorry, i shall lose all my needed fields, too. All right, they came back as time goes.
Hmm -- no. The little arrow below "Remove all from history" removed all my written expressions only, but has no effect on the list of available fields (placeholders).
May be, will be not a wrong practice from time to time do a clean reinstall, preserving only actions, genres and so on? (Probably all, what is in Backup.)
Quite so.
And then there is the function "Reset tag-fields" which should lead to a list that shows only the standard fields as supported by MP3tag.
I can not see such. Where is it? I can not see "Reset tag-fields" arrow anywhere. Just a moment, take a new snapshot. Here it is:

I think you did. The list you are showing isn't the list I thought of. I looked for the selection of fields and this list looks completely different. In your selection list of format-strings tag-fields are never shown with a leading underscore, only if you used the format-string yourself.
And do you know about that "Reset tag-fields" narrow, where is it?
The functions in the right-arrow-menu for fields are ...
(see the language file for the strings in your language):
_M_STR_TAGFIELDS_REMOVE Remove field
_M_STR_TAGFIELDS_REMOVEALL Remove all fields...
_M_STR_TAGFIELDS_RESET Reset fields...
Yes, i have them, too (when using english), as there it seems above, on my third screenshot. And it does nothing with the list.
(Now i try clean install, then fill back MySettings.zip plus individual translation file and flag.)
First attempt of clean install. I uninstalled Mp3tag. The uninstaller offered me to preserve the individual settings, and i select it. Fresh install. The result: no change, "_separator" is still there.
Second attempt. I uninstalled Mp3tag, also my settings. Fresh install. The result is proper, "_separator" disappeared. Then fill back my settings from previously taken Mp3tagSettings.zip, but without mp3tag.cfg. "_separator" is there, again.
There will be no third attempt. I also refill back the config file, and that is all. The _separator (by the way, in 2 copies, as it was earlier) and all the list remains, as it was -- what could i do?
You can stop now. It's probably a bug and I'll look into it and fix it when I find something.
My guess is that you're using _SEPARATOR
somewhere on the Tag Panel and it isn't filtered out when filling the list of standard tag fields.
Florian, thank you for your attention. Factually it is not a big bug , so anyway, it is not urgent.