Describe what is ymin, ymax

[llrs]

Following this gist I discovered mean_se. However I think it is poorly documented.

Also the error is not informative if someone provides a vector for mult:

x <- rnorm(100)
mean_se(x, mult = c(1, 2)
## Error: Elements must equal the number of rows or 1

I open this draft PR to know if something like this would be welcomed.

[yutannihilation]

Looks good to me!

Before I merge this, I need to ask you one more thing. Tidyverse team is trying to change the license of ggplot2 to more permissive one (the MIT license) to minimize the problems and confusions arising from license incompatibilities. If you are fine that your contribution will be merged to ggplot2 and get licensed under MIT, would you mind commenting "I agree" on #4281?

For more details, you can join the discussion on #4236.

[llrs]

I've been following the relicensing, and asked several questions on the usethis relicensing issue. I am still waiting for the blog post #4236 (comment) announced on October.

[yutannihilation]

Thanks for commenting there. Year, I too have been waiting for the blog post...

[yutannihilation]

Anyway, thanks for your contribution!