Contour plot colorscale domain smaller than [zmin, zmax] when contours.coloring is "fill" or "lines"

[lvlte]

Except for the 'heatmap' contour coloring, there seems to be no way to make the colorscale domain fit a fixed range [min, max], whether by setting zmin/zmax or coloraxis cmin/cmax.

For example (cf. https://codepen.io/lvlte/pen/jOejjRE), having z values ranging from 0 to 100, and contour levels from 10 to 90 with a size of 10 :

• with contours.coloring: "fill", the calculated colorscale domain is [5, 95], excluding zmin and zmax, which can be misleading when we expect the domain to be representative of the actual range of values in z, or any user-defined range set via zmin/zmax or cmin/cmax (adding explicit tickvals to force expand the domain doesn't change anything);
  

• with contours.coloring: "lines", the colorscale domain is [10, 90] : same problem as above but in addition the colorbar lines for level 10 and 90 are confounded with the borders;
  

• with contours.coloring: "heatmap", the colorscale domain is [0, 100] as expected;