$x{1}{2} is syntactically equivalent to $x{1}->{2}, just like $y[1][2] is $y[1]->[2] (and all combinations thereof). When the interpreter encounters multiple keys or indices in a row, it automatically includes the dereference operation. Since multi-dimensionality is always handled in the same way (AoA), there is no possible ambiguity so there is no risk in supporting both. See perlref and perllol for more info.