Looks good to me.

That said, I think this code can be further optimized:

} else if (element.equals("R") || (!element.isEmpty() && element.charAt(0) == 'R')) {

I think we only have to ask if R is the first char, not? That's the case if the element is exactly "R" too.

@johnmay, okay with the PR too?

@egonw startsWith is correct as it can be 'R', 'R#' or 'R1', 'R2' etc.

Patch looks good to merge