You can now specify the domain of the quadtree upon construction, such that you
can add points to the quadtree dynamically later. The quadtree example now also
shows how to do a quick rectangular search using the quadtree.
This makes the quadtree implementation more compatible with the force layout.
This change is backwards-compatible; if the points are not specified as x+y
objects, they are assumed to be tuples and converted to objects.
The data join is now specified as a single function of data, as with all other
properties. This allows the key to be computed on the previously-bound data,
rather than requiring the key to be serialized into the DOM (say, as an
attribute). In the case that there is no previously-bound data, it is still
possible to access the associated node as the `this` context.
The `enter` operator no longer performs an append. For symmetry with the `exit`
operator, you must call `append` after obtaining the entering selection. This
requires a tiny bit more code, but should make the code more clear. Also, it
provides an opportunity to use a different instantiation operator, such as the
new `insert` operator. This takes a second argument, which is a selector for the
insert-before reference element. For example, the selector ":first-child" will
prepend nodes.
The `empty` operator allows you to query whether a selection is empty (i.e.,
contains zero matching nodes).
Mike Bostock