$hash{key}= 'value';

##</code><code>##

    no autovivify;
    my %hash;
    # Examples of normal key insertion:
    $hash{key1}= 'value';       # succeeds
    $hash{key2}= {};            # succeeds
    $hash{key2}{key3}= 'value'; # succeeds
    # Examples of autovivification:
    $hash{key4}{key3}= 'value'; # should fail!
    $hash{key5}[0]= 1;          # should fail!