TikZ provides graphical layers on TikZ: "behind", "above" and "glass"
Description
TikZ-layers is a tiny package that provides, along side
"background", typical graphical layers on TikZ: "behind",
"above" and "glass". The layers may be selected with one of the
styles "on behind layer", "on above layer", "on glass layer" as
an option to a {scope} environment.
