Update README

Author: mbostock

README.md

@@ -687,7 +687,7 @@ If **x2** is not specified, it defaults to **x1**. If **y2** is not specified, i
 
 By default, the data is assumed to represent a single series (a single value that varies over time, *e.g.*). If the **z** channel is specified, data is grouped by *z* to form separate series. Typically *z* is a categorical value such as a series name. If **z** is not specified, it defaults to **fill** if a channel, or **stroke** if a channel.
 
-The **stroke** defaults to none. The **fill** defaults to currentColor if the stroke is none, and to none otherwise. If both the stroke and fill are defined as channels, or if the *z* channel is also specified, it is possible for the stroke or fill to vary within a series; varying color within a series is not supported, however, so only the first channel value for each series is considered. This limitation also applies to the **fillOpacity**, **strokeOpacity**, **strokeWidth**, **title**, and **ariaLabel** channels.
+The **stroke** defaults to none. The **fill** defaults to currentColor if the stroke is none, and to none otherwise. If the fill is defined as a channel, the area will be broken into contiguous overlapping segments when the fill color changes; the fill color will apply to the interval spanning the current data point and the following data point. This behavior also applies to the **fillOpacity**, **stroke**, **strokeOpacity**, **strokeWidth**, **opacity**, **href**, **title**, and **ariaLabel** channels. When any of these channels are used, setting an explicit **z** channel (possibly to null) is strongly recommended. The **strokeLinecap** and **strokeLinejoin** default to *round*, and the **strokeMiterlimit** defaults to 1.
 
 Points along the baseline and topline are connected in input order. Likewise, if there are multiple series via the *z*, *fill*, or *stroke* channel, the series are drawn in input order such that the last series is drawn on top. Typically, the data is already in sorted order, such as chronological for time series; if sorting is needed, consider a [sort transform](#transforms).
 
@@ -947,7 +947,7 @@ In addition to the [standard mark options](#marks), the following optional chann
 
 By default, the data is assumed to represent a single series (a single value that varies over time, *e.g.*). If the **z** channel is specified, data is grouped by *z* to form separate series. Typically *z* is a categorical value such as a series name. If **z** is not specified, it defaults to **stroke** if a channel, or **fill** if a channel.
 
-The **fill** defaults to none. The **stroke** defaults to currentColor if the fill is none, and to none otherwise. If both the stroke and fill are defined as channels, or if the *z* channel is also specified, it is possible for the stroke or fill to vary within a series; varying color within a series is not supported, however, so only the first channel value for each series is considered. This limitation also applies to the **fillOpacity**, **strokeOpacity**, **strokeWidth**, and **title** channels. The **strokeWidth** defaults to 1.5 and the **strokeMiterlimit** defaults to 1.
+The **fill** defaults to none. The **stroke** defaults to currentColor if the fill is none, and to none otherwise. If the stroke is defined as a channel, the line will be broken into contiguous overlapping segments when the stroke color changes; the stroke color will apply to the interval spanning the current data point and the following data point. This behavior also applies to the **fill**, **fillOpacity**, **strokeOpacity**, **strokeWidth**, **opacity**, **href**, **title**, and **ariaLabel** channels. When any of these channels are used, setting an explicit **z** channel (possibly to null) is strongly recommended. The **strokeWidth** defaults to 1.5, the **strokeLinecap** and **strokeLinejoin** default to *round*, and the **strokeMiterlimit** defaults to 1.
 
 Points along the line are connected in input order. Likewise, if there are multiple series via the *z*, *fill*, or *stroke* channel, the series are drawn in input order such that the last series is drawn on top. Typically, the data is already in sorted order, such as chronological for time series; if sorting is needed, consider a [sort transform](#transforms).