Indexes can be values of any scalar type, incl. strings.

This provides both scalar and associative arrays (hash tables).

E.g.

$a[0] = "abc";  $a[1] = 'def';  $a[2] = ghi;

$b['abc'] = 0;  $b[def] = 1;    $b["ghi"] = 2;

Internally, all indexes are treated as strings, so PHP really has only hash tables.