Spanner label for rows

[bfletcherjohnson]

Trying to create a detailed confusion matrix, something like:

It would be helpful to allow a spanner label for rows, to allow placement of the "ACTUAL" spanner label in the image. I understand how to do the spanner label for columns, the "PREDICTED" in the image.
Or is it already possible to add a row spanner label? The "ROW GROUP LABEL" really doesn't quite satisfy the need.

[bfletcherjohnson]

Ha, I see that a similar request has been made for rstudio gt. https://github.com/rstudio/gt/issues/577