Limits for friction and restitution

Hi,

Can you please advice on what the upper and lower limits are for the friction coefficient and restitution coefficient in pybullet. 
I was under the impression that the limits would be 0 to 1. However, upon reading some of the forum posts on the bullet forum it seems that values can go beyond 1. Would you still say that 0 and 1 realistic lower and upper limits? 
