Having an AltGr (third-level chooser) key on my native language keyboard, I was quite surprised to see Ubuntu (Linux in general? It's all in xkb's symbols layou

Having an AltGr (third-level chooser) key on my native language keyboard, I was quite surprised to see Ubuntu (Linux in general? It's all in xkb's symbols layout anyway) have not only third level glyphs on way more keys than I was used to from Windows (AltGr+Q = @, AltGr+E = €, etc) but also fourth level glyphs (AltGr+Shift+...). Sadly a lot of them are pretty useless (e.g. the many "logical negation" keys -- I guess they used them in place of None).