However Git allows to salvage the history of SVN during the migration, probably because SVN was one of the most popular CVS before itself. One would expect that

However Git allows to salvage the history of SVN during the migration, probably because SVN was one of the most popular CVS before itself. One would expect that if something dethrones Git, it would (have to) do the same. That said, that method is not really viable if the piece of code moves too much. I would then side with the other suggestion to put that in a separate file in a doc/ sub-folder and just refer to that file in a comment. I guess that for most programming editors, "open file under cursor" is just a key combo away.