[fpc-pascal] Why do string indices start at 1, but array indices start at 0?

[Marco van de Voort]

In our previous episode, Jonas Maebe said:
> > During compilation, by statically checking the indices used to access the
> > string, the compiler could fire a warning (or error?) if a  string[0] is
> > found.
> 
> The compiler already does that (except for shortstrings, where string[0] is valid).

Isn't the warning mode dependent? Delphi warns, or at least it did in older
versions.