main::(-e:1):   0
  DB<1> x <Prefix1={A,B}:{c,d}>
0  'Prefix1=A:c'
1  'Prefix1=A:d'
2  'Prefix1=B:c'
3  'Prefix1=B:d'
  DB<2> @keys = <Prefix1={A,B}:{c,d}>

  DB<3> @hash{@keys} = ('value1') x @keys