snl shall be the root of a grove. transform-grove creates
a new grove from snl by adding a transform-args property to
the grove root whose value is a list containing obj, , and
returns an object of type transform-grove-spec specifying the
transformation of that new grove.
(select-grove nl obj)
Returns a node-list containing those members of nl whose grove
root has a transform-args property that contains a member equal
to obj.