In rgl, each window contains a tree of “subscenes”, each containing views of
a subset of the objects defined in the window.
Rendering in each subscene depends on the viewport, the projection, and the model
transformation. Each of these characteristics may be inherited from the parent
(embedding[i] = "inherit"
), may modify the parent (embedding[i] = "modify"
),
or may replace the parent (embedding[i] == "replace"
). All three must be
specified if embeddings
is used.