You're right. It's tabs and spaces. That's exactly why it's important to write it down (complete with pros/cons and links), and end the debate. That's why I think it's a good idea to put it in the rules - so you don't keep going around and around on it. I'm not convinced there is an obviously-right answer (i.e., one that you'll get everyone to facepalm and say, "of course, that's right!"), which means you'll always get pushback. But if it's written down, explanation given, you'll probably at least find acceptance from those who disagree, and can move on to being actually productive.
Of course, running your code through perltidy before checking it in (or, better yet, having the VCS running the code through whichever tidy tool is appropriate) is even better. But, even then, you'll have to explain why your tidy tools are doing this, so that those who disagree with the formatting option can be, well, silenced, if not assimilated. Otherwise, every time you hire a new person, you'll have to explain it all over again, even if it's automated via perltidy or whatever.