Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -1,5 +1,21 @@
 # Observable Plot - Changelog
 
+## 0.6.6
+
+[Released April 26, 2023.](https://github.com/observablehq/plot/releases/tag/v0.6.6)
+
+*Pssst… Plot has a brand-new documentation website. It is coming soon—stay tuned!*
+
+The [image mark](./README.md#image) can now generate circular images with the **r** channel, and rotate images with the **rotate** channel.
+
+The [axis mark](./README.md#axis) now properly respects the **margin** shorthand option, changing the default for **marginTop**, **marginRight**, **marginBottom**, and **marginLeft**. The axis mark now correctly renders the axis label when the **href** option is used, or any other option that may be interpreted as a channel.
+
+Facet scale domains are now imputed correctly when the **sort** mark option is used with a **limit**, or otherwise causing the facet domain to be truncated. Plot no longer generates a spurious warning when faceting and using non-array data, such as an Arquero table. The **interval** scale option, when expressed as a fractional number such as 0.2, now has better floating point precision.
+
+The [Plot.indexOf](./README.md#plotindexof) channel transform, used internally by some mark shorthand, is now exported.
+
+Plot has a few improvements for server-side rendering. Plot now assumes a high pixel density display when headless. The default class name for plots is now deterministically generated (`plot-d6a7b5`) rather than randomly generated; this makes it easier to apply overrides to Plot’s default styles with an external stylesheet. (The default class name will change if Plot’s default styles change in a future release.) The **className** plot option is now inherited by a plot’s legends, if any. The density mark now respects the Plot’s **document** option, and the **caption** option now uses a duck test instead of testing against the global Node.
+
 ## 0.6.5
 
 [Released April 1, 2023.](https://github.com/observablehq/plot/releases/tag/v0.6.5)

README.md

@@ -2798,6 +2798,10 @@ This channel helper returns a source array as-is, avoiding an extra copy when de
 Plot.raster(await readValues(), {width: 300, height: 200, fill: Plot.identity})
 ```
 
+#### Plot.indexOf
+
+This channel helper returns an array of numbers [0, 1, 2, 3, …]. It is used internally by marks with zero-based index defaults for channels.
+
 ## Initializers
 
 Initializers can be used to transform and derive new channels prior to rendering. Unlike transforms which operate in abstract data space, initializers can operate in screen space such as pixel coordinates and colors. For example, initializers can modify a marks’ positions to avoid occlusion. Initializers are invoked *after* the initial scales are constructed and can modify the channels or derive new channels; these in turn may (or may not, as desired) be passed to scales.