strokeWidth channel example

Author: Fil

CHANGELOG.md

@@ -25,6 +25,12 @@ The [Plot.marks(...*marks*)](https://github.com/observablehq/plot/blob/main/READ
 
 All marks now support the [shapeRendering option](https://developer.mozilla.org/en-US/docs/Web/SVG/Attribute/shape-rendering). (This is a constant; it may not vary across marks.) All marks now allow strokeWidth to be specified as a channel. Text marks now also allow stroke and strokeOpacity to be specified as channels. If its fill is not *none*, a line’s default stroke is now *none* rather than *currentColor*, making it consistent with dot and other marks. When a fill or fillOpacity channel is used with a link, or when a stroke or strokeOpacity channel is used with a rule, undefined values will now be filtered. The text mark now uses attributes instead of styles for font rendering properties, improving compatibility with Firefox.
 
+<img width="640" alt="a series of dots with an increasing stroke width" src="https://user-images.githubusercontent.com/7001/130228992-eb2452f1-8822-4239-87b7-07f79e5a2ccb.png">
+
+```js
+Plot.dotX(d3.range(41), { strokeWidth: (d) => (1 + d) / 15 }).plot()
+```
+
 Marks that represent continuous intervals (rect, bar, and rule) now handle collapsed domains during rendering. A domain is considered collapsed when it contains only a single value. A collapsed domain can occur when all input values to the bin transform are equal (*e.g.*, [1, 1, 1, …] produces a domain of [1, 1]). Previously a collapsed domain would result in an invisible zero-width mark; now the mark spans the full extent of the chart.
 
 <img width="640" alt="a histogram with a collapsed domain showing a single bar that represents the value 1 with frequency 3" src="https://user-images.githubusercontent.com/230541/130156841-d888e397-0040-4aef-bbb5-9ff19e1e3389.png">