does anyone have any specific information regarding the legal requirements of a fender on a bike?

from what i've seen/heard:
- signals must be wider than plate
- plate must be lit and "clearly visible from behind" (although 'visible is open to interpretation from some mods i've seen.. )

although that's all just hearsay... anyone with concrete knowledge?

i'm planning on doing some mods, and would like to know how radical i can get...

thanks in advance