Thread:Koppadasao/@comment-26828130-20180607142520/@comment-1744236-20180607210413

That is the manual, and you find the #sub-#pos/#rpos problem by comparing the output of the #pos/#rpos function with the notes on the #sub function. It’s rather deeply hidden, though

And I just noticed that the solution I used is actually provided in the text of the #rpos function. If I had noticed that when I worked it out, I wouldn’t have needed the extra step to check if I got it right