Nice to see I was right on the bull's eye with that one. As for TRON, my reasoning for it is a bit different. Since users in the Grid (As Kevin Flynn shows in the movie) will actually bleed when cut, I felt it could be necessary to have a higher rating, so that people are allowed to be descriptive. Programs simply "derezz" when hit, so less issues there. As for sexual themes, I think the only thing happening there is possible romance. Of course, don't expect anything serious. I think the only "Alcohol and Drugs" reference would be the cyber-alcohol Castor drinks in TRON: Legacy. So honestly, I might have been able to put it as T rating, but I wanted more open possibilities.
I guess it's like Zerin says. The ratings are mostly to warn the readers/players about the content but of course there's no way to make sure that 10 year olds don't read M rated roleplays. Ratings don't forbid you to enter a roleplay here, but they make sure that you know what you're getting yourself into. And they are a way for the GM to make sure that the RP doesn't get a theme that they wouldn't want it to get.
I have set the rating as K+ for some of my RPs and that works fine, but most people seem to prefer the T rating since they don't have to think much about how much violence is allowed then. Difference between M and T should pretty much be how much descriptive violence and references to things like alcohol and drugs there may be. "Romance" past the T rating shouldn't really exist on a pokémon forum, in my opinion ._. By romance, I guess I mean adult themes.
It would be a great thing if you could explain/summarize it to players. pokepokemo signed up but he doesn't know much of anything TRON. I've seen both TRON movies too (I almost cried from the over-powering extraordinary effects on Legacy), but I can't find a way to explain the grid and it's entirety without taking an hour of text to do so.If you feel the need to have someone help explaining, I might be able to. I've seen both movies and I did plan a TRON RP some ways back but never posted it. It's a cool world.
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By the way...
Have you ever seen or made an UNRATED or M+ Roleplay? If so, what was it?