It would be very helpful to be able to add outlines to text layers. This allows for text to be legible on any background (eg white text with black outline, or black text with white outline).

Also, though not strictly related, there does not seem to be any documentation of the options "familysrc", "sizesrc", or "colorsrc" anywhere.
https://plot.ly/javascript/reference/#bar-textfont
https://plot.ly/r/reference/#scatter-textfont

Related: talgalili/heatmaply#42