I'm modifying taskbar to show only floating or minimized windows. I know that there are ICCCM and EWMH standards. Can I use them to check whether window is floating or tiled? Or is there something else that I can use?
I don't want to do it specifically for window manager, because I'm about to switch to another.
Nope, floating / tiled is nothing that EWMH or ICCCM defines.