Update CHANGES.

CHANGES.md

@@ -670,7 +670,7 @@ Mention d3-scale-chromatic?
 
 ## [Selections (d3-selection)](https://github.com/d3/d3-selection/blob/master/README.md)
 
-Selections no longer subclass Array using [prototype chain injection](http://perfectionkills.com/how-ecmascript-5-still-does-not-allow-to-subclass-an-array/#wrappers_prototype_chain_injection); they are now plain objects, improving performance.
+Selections no longer subclass Array using [prototype chain injection](http://perfectionkills.com/how-ecmascript-5-still-does-not-allow-to-subclass-an-array/#wrappers_prototype_chain_injection); they are now plain objects, improving performance. The internal fields (*selection*.\_groups, *selection*.\_parents) are private; please use the documented public API to manipulate selections. The new [*selection*.nodes](https://github.com/d3/d3-selection#selection_nodes) method generates an array of all nodes in a selection.
 
 Selections are now immutable: the elements and parents in a selection never change. (The elements’ attributes and content will of course still be modified!) The [*selection*.sort](https://github.com/d3/d3-selection#selection_sort) and [*selection*.data](https://github.com/d3/d3-selection#selection_data) methods now return new selections rather than modifying the selection in-place. In addition, [*selection*.append](https://github.com/d3/d3-selection#selection_append) no longer merges entering nodes into the update selection; use [*selection*.merge](https://github.com/d3/d3-selection#selection_merge) to combine enter and update after a data join. For example, the following [general update pattern](http://bl.ocks.org/mbostock/a8a5baa4c4a470cda598) in 3.x:
 
@@ -740,7 +740,7 @@ There is now only one class of selection. 3.x implemented enter selections using
 
 The [*selection*.data](https://github.com/d3/d3-selection#selection_data) method has been changed slightly with respect to duplicate keys. In 3.x, if multiple data had the same key, the duplicate data would be ignored and not included in enter, update or exit; in 4.0 the duplicate data is always put in the enter selection. In both 3.x and 4.0, if multiple elements have the same key, the duplicate elements are put in the exit selection. Thus, 4.0’s behavior is now symmetric for enter and exit, and the general update pattern will now produce a DOM that matches the data even if there are duplicate keys.
 
-Selections have several new methods! Use [*selection*.raise](https://github.com/d3/d3-selection#selection_raise) to move the selected elements to the front of their siblings, so that they are drawn on top; use [*selection*.lower](https://github.com/d3/d3-selection#selection_lower) to move them to the back. Use [*selection*.dispatch](https://github.com/d3/d3-selection#selection_dispatch) to dispatch a [custom event](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent) to event listeners. Use [*selection*.nodes](https://github.com/d3/d3-selection#selection_nodes) to generate an array of all nodes in a selection.
+Selections have several new methods! Use [*selection*.raise](https://github.com/d3/d3-selection#selection_raise) to move the selected elements to the front of their siblings, so that they are drawn on top; use [*selection*.lower](https://github.com/d3/d3-selection#selection_lower) to move them to the back. Use [*selection*.dispatch](https://github.com/d3/d3-selection#selection_dispatch) to dispatch a [custom event](https://developer.mozilla.org/en-US/docs/Web/API/CustomEvent) to event listeners.
 
 When called in getter mode, [*selection*.data](https://github.com/d3/d3-selection#selection_data) now returns the data for all elements in the selection, rather than just the data for the first group of elements. The [*selection*.call](https://github.com/d3/d3-selection#selection_call) method no longer sets the `this` context when invoking the specified function; the *selection* is passed as the first argument to the function, so use that. The [*selection*.on](https://github.com/d3/d3-selection#selection_on) method now accepts multiple whitespace-separated typenames, so you can add or remove multiple listeners simultaneously. For example: