For those adventurous souls who are already using Oniguruma...

With the following Oniguruma re:

   print  "aabb".index(/.+?(?<!a)/)
   print "\n"

My reasoning tells me I should be getting 3, but I'm getting 0.  
Basically, the .+ should force the re 'cursor' past at least the first  
a; after that, the negative lookback should force it past the first b.  
Could someone explain where I'm misunderstanding?

Thanks,
Ken