I'd prefer it if I could sort the series and then the title.
To work around the lack of being able to do that I changed the titles of my books like PeterT suggested ({series:re(([^\s])[^\s]+(\s|$),\1)}{series_index:0>2s| - | - }{title}) Thanks for that!
Sadly I only get the first letter of each word in the series. If the series have only got one word like eg Twilight I think, as my library grows, there will soon be another series starting with the same letter and the series will be mixed.
Is it possible to pick the first two or three letters? I added a 3 in different places of the code and got
strange
results...