Update README.

README.md

@@ -806,17 +806,19 @@ Renders this symbol type to the specified *context* with the specified *size* in
 
 [<img alt="Stacked Bar Chart" src="https://raw.githubusercontent.com/d3/d3-shape/master/img/stacked-bar.png" width="295" height="154">](http://bl.ocks.org/mbostock/3886208)[<img alt="Streamgraph" src="https://raw.githubusercontent.com/d3/d3-shape/master/img/stacked-stream.png" width="295" height="154">](http://bl.ocks.org/mbostock/4060954)
 
-Some shape types can be stacked, placing one shape adjacent to another. For example, a bar chart of monthly sales might be broken down into a multi-series bar chart by product category, stacking bars vertically. This is equivalent to subdividing a bar chart by an ordinal dimension (such as product category) and applying a color encoding. Stacked charts can show overall value and per-category value simultaneously; however, it is typically harder to compare across categories, as only the bottom layer of the stack is aligned. (See also [grouped charts](http://bl.ocks.org/mbostock/3887051).)
+Some shape types can be stacked, placing one shape adjacent to another. For example, a bar chart of monthly sales might be broken down into a multi-series bar chart by product category, stacking bars vertically. This is equivalent to subdividing a bar chart by an ordinal dimension (such as product category) and applying a color encoding.
 
-Like the [pie generator](#pies), the stack generator does not produce a shape directly. Instead it computes a layout which you can then pass to an [area generator](#areas) or use directly, say to position bars.
+Stacked charts can show overall value and per-category value simultaneously; however, it is typically harder to compare across categories, as only the bottom layer of the stack is aligned. So, chose the [stack order](#stack_order) carefully, and consider a [streamgraph](#orderWiggle). (See also [grouped charts](http://bl.ocks.org/mbostock/3887051).)
+
+Like the [pie generator](#pies), the stack generator does not produce a shape directly. Instead it computes positions which you can then pass to an [area generator](#areas) or use directly, say to position bars.
 
 <a name="stack" href="#stack">#</a> <b>stack</b>()
 
 Constructs a new stack generator with the default settings.
 
 <a name="_stack" href="#_stack">#</a> <i>stack</i>(<i>data</i>[, <i>arguments…</i>])
 
-Generates a stack for the given array of *data*, returning an array representing each series. Any additional *arguments* are arbitrary; they are simply propagated to the [keys accessor](#stack_keys) along with the `this` object.
+Generates a stack for the given array of *data*, returning an array representing each series. Any additional *arguments* are arbitrary; they are simply propagated to accessors along with the `this` object.
 
 The series are determined by the [keys accessor](#stack_keys); each series *i* in the returned array corresponds to the *i*th key. Each series is an array of points, where each point *j* corresponds to the *j*th element in the input *data*. Lastly, each point is represented as an array [*y0*, *y1*] where *y0* is the lower value (baseline) and *y1* is the upper value (topline); the difference between *y0* and *y1* corresponds to the computed [value](#stack_value) for this point. The key for each series is available as *series*.key, and the [index](#stack_order) as *series*.index. The input data element for each point is available as *point*.data.