Subbase constraints

[jsantell]

From Roblox article on IK:

Currently multiple chains can connect to a parent chain on one of the parent chain's joints. They share the joint and bone where the two chains connect. If there's a chain of constrained joints n units long, and there are two subchains x and y connected at the n / 2th joint:

                   x
                  /
o->o->o->o->o->o->o
                  \
                    y

What determines which angle joints x and y can rotate, since the main chain's direction is being oriented by it's own target? This is also the reason why IKHelper does not render subbases correctly.