expand on comment

Author: samhinshaw

src/plot_api/plot_api.js

@@ -3675,7 +3675,17 @@ function makePlotFramework(gd) {
         // The plot container should always take the full with the height of its
         // parent (the graph div). This ensures that for responsive plots
         // without a height or width set, the paper div will take up the full
-        // height & width of the graph div.
+        // height & width of the graph div. 
+        // So, for responsive plots without a height or width set, if the plot
+        // container's height is left to 'auto', its height will be dictated by
+        // its childrens' height. (The plot container's only child is the paper
+        // div.) 
+        // In this scenario, the paper div's height will be set to 100%,
+        // which will be 100% of the plot container's auto height. That is
+        // meaninglesss, so the browser will use the paper div's children to set
+        // the height of the plot container instead. However, the paper div's
+        // children do not have any height, because they are all positioned
+        // absolutely, and therefore take up no space.
         .style({
             width: "100%",
             height: "100%"