In lyrics Alt+255 does the same as underscore shown as space when it is checked. When you have unchecked this item then you can use Alt+255 instead.
Alt-255 used to be good fun in the Dos-days.
In modern Dos-boxes it does not work anymore: you could have a file like Holy<alt-255>Cow.txt which showed in the directory as "Holy Cow.txt" - and nobody could find it.
Worse still, a filename could consist of a single Alt-255 - and you would hardly notice it.
But hey, old hat - and a discarded hat, at that.
Having said that, 255 (as the highest possible number in 16 bits) may still serve as a special character, and you have found it.
Alt-0255 is quite different: a 4-digit code denotes a Unicode character.
For instance, Alt-128 is simply a character of the old Dos Ascii-set, whereas Alt-0128 is the Euro-symbol €. Hey.
Well, that's about enough for a side note.
So true... or else it would be 65535 (unsigned integer)
It might make for a good character to use in a password (if you don't forget it).