aa_allow:   /* innermost frame allows a */
  aa_block:     /* innermost frame denies a */
  aa2_block:     /* innermost frame (view-source: URL) denies a */
  ab_allow:     /* innermost frame allows a */
  ab_block:     /* innermost frame denies a */
  aba_allow:    /* innermost frame allows b,a */
  aba_block:    /* innermost frame denies b */
  aba2_block:   /* innermost frame denies a */
  abb_allow:    /* innermost frame allows b,a */
  abb_block:    /* innermost frame denies b */
  abb2_block:   /* innermost frame denies a */