In that case I'd prefer to see that in the documentation or a comment. By "using" a version number you are not merely saying "I've tested this only with this particular version." What you are effectively saying is more like "I believe this will not work with anything older than X."
If I see "use 5.12.4;" I assume there was something wrong with even 5.12.3, something that prevents the code to work correctly. So probably I would not bother trying to run it under 5.10.x. On the other hand with a comment about the version tested under, I would try it and only if I end up getting an error I'd take the possible version differences into account.
Jenda
Enoch was right!
Enjoy the last years of Rome.