Add example showing how to set the zorder via order sorting

examples/specs/selection_type_point_zorder.vl.json

@@ -0,0 +1,25 @@
+{
+  "data": {
+    "url": "https://cdn.jsdelivr.net/npm/[email protected]/data/cars.json"
+  },
+  "mark": {"type": "circle", "opacity": 1},
+  "encoding": {
+    "color": {
+      "condition": {"param": "param_122", "value": "coral", "empty": false},
+      "value": "grey"
+    },
+    "order": {
+      "value": 0,
+      "condition": {"param": "param_122", "value": 1, "empty": false}
+    },
+    "size": {
+      "condition": {"param": "param_122", "value": 400, "empty": false},
+      "value": 100
+    },
+    "x": {"field": "Horsepower", "type": "quantitative"},
+    "y": {"field": "Miles_per_Gallon", "type": "quantitative"}
+  },
+  "params": [
+    {"name": "param_122", "select": {"type": "point", "on": "mouseover"}}
+  ]
+}

site/docs/encoding.md

@@ -413,7 +413,7 @@ The key channel can enable object constancy for transitions over dynamic data. W
 
 ## Order Channel
 
-`order` channel can define a data field (or a ordered list of data fields) that are used to sorts stacking order for stacked charts (see [an example in the `stack` page](stack.html#order)) and the order of data points in line marks for connected scatterplots (see [an example in the `line` page](line.html#connected-scatter-plot)).
+`order` channel can define a data field (or a ordered list of data fields) that are used to sorts stacking order for stacked charts (see [an example in the `stack` page](stack.html#order)), the order of data points in line marks for connected scatterplots (see [an example in the `line` page](line.html#connected-scatter-plot)), and which data points are plotted on top in a chart (the "zorder", see [an example in the gallery]({{ site.baseurl }}/examples/selection_type_point_zorder.html)).
 
 {% include table.html props="order" source="Encoding" %}