What is the smoothing method used in type "contour" with plotly in R?

I am making a contour plot in R using plotly. I want to know what smoothing method is used (is it loess or something different?)

All the documentation I could find was that:

• You can set smoothing as a number between or equal to 0 and 1.3 (default = 1)
• Description: It sets the amount of smoothing for the contour lines, where "0" corresponds to no smoothing.

My code:

m <- matrix(data = rnorm(56), ncol = 8, nrow = 7) plot_ly(z = m, type = "contour")

My results: Contour plot

Thank you! Joan