I am plotting a 3D chart with three variables, which are date, diffusion, and avg_Entropy. I would like to insert a simple 2D plane horizontally into the scatter plot that will serve as a threshold for diffusion. I have served multiple forums and tutorials for such an implementation, and all I can find is how to insert a regression line which is not really what I want. I would like to be able to, for example, insert a transparent plane through the 100 value for “diffusion” so that any points above this threshold meet the criteria for my experiment. Here is my current code.

```
plot_ly(color = ~factor(date), showlegend = T) %>%
add_markers(data = tweets, x = ~date, y = ~avg_Entropy, z = ~diffusion) %>%
add_paths(data = tweets, x = ~date, y = ~avg_Entropy, z = ~diffusion)
```