Update README.md

Author: mbostock

README.md

@@ -536,7 +536,7 @@ svg.selectAll("circle")
 
 You can pass a third function for exit, too. The returned enter and update selections are again merged and returned by *selection*.join. By separating enter and update, and by specifying a key function to [*selection*.data](#selection_data), you can minimize changes to the DOM to optimize performance.
 
-You also animate enter, update and exit by creating transitions inside the *enter*, *update* and *exit* functions. To avoid breaking the method chain, use *selection*.call to create transitions, or return an undefined enter or update selection to prevent merging: the return value of the *enter* and *update* functions is important, as it specifies the two selections to merge and return by *selection*.join.
+You also animate enter, update and exit by creating transitions inside the *enter*, *update* and *exit* functions. To avoid breaking the method chain, use *selection*.call to create transitions, or return an undefined enter or update selection to prevent merging: the return value of the *enter* and *update* functions specifies the two selections to merge and return by *selection*.join.
 
 For more, see the [*selection*.join notebook](https://observablehq.com/@d3/selection-join).