Documented isVisibleElement hook
Better comments
Merge commit 'd6552bf9e6be9edae4c3fb173ff4d8c72ef663a4' into 3.2
Merge branch '3.2' into 3.2-ja.
Catch up to 537c8d30025f8f0f4a54d02c2d5de4f382d3603d.