/* Record "guard" in "graft" so that it will be enforced somewhere
* up the tree. If the graft already has a guard, then it may be partially
* redundant in combination with the new guard and in the context
/* Record "guard" in "graft" so that it will be enforced somewhere
* up the tree. If the graft already has a guard, then it may be partially
* redundant in combination with the new guard and in the context