The problem in this case (as with most issues regarding `@inbounds`) is that this text was written before arrays with non-standard indices existed in Julia. So

The problem in this case (as with most issues regarding `@inbounds`) is that this text was written before arrays with non-standard indices existed in Julia. So the example was correct at the time it was written, just like the StatsBase code was correct. Old code needs careful checking to fix all these occurrences.