These realize the common implementation of SphereCollision: traversing down the octree nodes. They take care of traversing down the non-leaf nodes, you only have to override the CommonXxxLeaf versions where you handle the leaves (and you have to call CommonXxx from normal Xxx routines).
Note that methods here do not try to limit detected intersections to their boxes. If you will insert a large triangle into a node, that is partially inside and partially outside of this node, the collision methods may find an intersection outside of this node.
This is not be a problem for a root node, since the root node has a box such that every triangle is completely inside. But it is important to remember when you implement recursive *Collision calls in nodes: if you want to query your subnodes in some particular order (for example to honour ReturnClosestIntersection = True), then remember that one subnode may detect a collision that in fact happened in other subnode.