Yes, I know, but the problem is that xprop says nothing about window role in most apps. Some programs use that feature but most doesn't. It seems libreoffice doesn't. I wonder if there is a way to tweak that, like in conky where you can specify and set name, class, title or role at will. I'm afraid that's not posible or at least easy for common apps.
Since role doesn't seem to be an option for libreoffice, I guess I'll need to play with window names, titles and classes and see what i can get. Thanks anyway, PackRat. Your advice is always welcome.