How do I edit the iTunes Compilation tag?

I can see the %ITUNESCOMPILATION% tag in the Foobar2000's properties but not in MP3Tag's Extended Tags; it just shows up as COMPILATION.

I'm guessing the iTunes Comp tag is left over from when I used iTunes years ago. So, when I add a 1 to the compilation field in MP3Tag, is it actually writing to the left over ITUNESCOMPILATION tag?

Thanks for any help!

Yes, the tag is updated correctly. The name in mp3tag is just a bit more friendly. But it is written to the correct tag field.

A good source for information about the fields in MP3tag is the documentation:

This will also reveal which token is used for the various target formats and that Foobar simply chose a different label for the same thing.

Thanks for the response.

So, what is the field literally called? I'm confused about whether Foobar2000 is representing the COMPILATION field as ITUNESCOMPILATION or is MP3Tag doing the reverse?

You can open one of your songs in a Hex Editor and see the name there.

In a MP3 file it would be TCMP

BTW:
This "translation"-mapping was already mentioned in the first answer from @ohrenkino.
Nobody can remember 4 letter abbreviations like TCMP for COMPILATION.
Therefore every tagging tool is using slighty different names but all write the data back into the same TCMP field in this example and for MP3 files.

I see. I think this is the part that was confusing me, I thought TCMP was a kind of tag or a remapping scheme, or something. Thanks for the clarification.

Is there a way to set the Tag Panel to write to a "Compilation" field and not the iTunes Compilation / TCMP field?

In MP3tag COMPILATION is the reserved name for the field as described earlier. So it is not possible to create a user-defined field with the same name.
What would be the purpose of this non-standard field?

This is only possible if you create a so called user-defined field like
MYCOMPILATION
or
COMPILATIONMRMECH
or something that is clearly different from the official
COMPILATION

The problem with user-defined fields is that they are not supported by most third-party software, like smartphone or car players.

Thanks for the explanation, LyricsLover. I'm just using it for sorting in Foobar2000.