Update CHANGELOG

Author: mbostock

CHANGELOG.md

@@ -1,5 +1,19 @@
 # Observable Plot - Changelog
 
+## 0.4.2
+
+*Not yet released. These are forthcoming changes in the main branch.*
+
+The new [box mark](./README.md#box) (TODO documentation) generates a horizontal or vertical boxplot suitable for visualizing one-dimensional distributions. It is a convenience mark that composites a rule, bar, tick, and dot.
+
+Plot’s shorthand syntax has been expanded. The [bar mark](./README.md#bar) now supports one-dimensional shorthand: if no *options* are specified, then Plot.barX and Plot.barY can be used to visualize an array of numbers. This shorthand also now applies to the [rect mark](./README.md#rect) and the [vector mark](./README.md#vector). The [area mark](./README.md#area) now supports two-dimensional shorthand: if no *options* are specified, then Plot.area can be used to visualize an array of [x, y] tuples (similar to Plot.line).
+
+The mark [sort options](./README.md#sort-options) now support implicit “width” and “height” channels, defined as |*x2* - *x1*| and |*y2* - *y1*| respectively. These channels are useful for sorting rects and bars by length. The *reverse* option defaults to true when sorting by these channels. When sorting by *y*, but not *y* channel is available, sorting will now fallback to sorting by *y2* if available; the same fallback logic applies to *x* and *x2*. (This behavior was previously supported on marks that support implicit stacking, but now applies universally to all marks.)
+
+The [bin transform](./README.md#bin) now supports *x* and *y* reducers, which represent the respective midpoint of the bin: (*x1* + *x2*) / 2 and (*y1* + *y2*) / 2 respectively. The [bin](./README.md#bin), [group](./README.md#group), and [window](./README.md#window) transforms now support percentile reducers of the form *pXX* where *XX* is a number in [00, 99]. For example *p25* represents the first quartile and *p75* represents the third quartile.
+
+The error message when attempting to create a standalone legend without a valid scale definition has been improved. The high cardinality warning for the implicit *z* channel has been relaxed; it is now only triggered if more than half of the values are distinct. When the axis *ticks* option is specified as null, no ticks are generated. When the axis *tickFormat* option is specified as null, no tick labels are generated.
+
 ## 0.4.1
 
 Released February 17, 2022.