Set whether axis ticks and gridlines are above or below most artists.
This controls the zorder of the ticks and gridlines. For more
information on the zorder see Zorder Demo.
Parameters:
b:bool or 'line'
Possible values:
True (zorder = 0.5): Ticks and gridlines are below all Artists.
'line' (zorder = 1.5): Ticks and gridlines are above patches
(e.g. rectangles, with default zorder = 1) but still below lines
and markers (with their default zorder = 2).
False (zorder = 2.5): Ticks and gridlines are above patches
and lines / markers.