OptionalstartThe lowest level drawn.
OptionalendThe highest level drawn; the walk stops at or before it.
OptionalsizeThe value between one level and the next.
Optionaltypelevels for the ordinary reading, constraint for the region-shading
one — which draws a boundary rather than a family of iso-curves, so its
start/end are the ends of an interval and not a level ladder.
OptionalshowlinesWhether the curves themselves are stroked, default true.
It decides whether the elements a contour is highlighted through exist at
all: createLines binds the level groups to no data when this is off, and
a labels-only trace has the group removed again once the labels are
placed. A fill-only contour is drawn entirely out of g.contourfill
paths, one per level with no per-curve element.
The levels a contour trace draws its curves at.
Plotly resolves all three during calc —
setContoursfills them in even when the author leftautocontouron — so a drawn chart states its own levels and nothing has to be guessed from the grid.