text: # tests of return value inversion
  # placeholder for future expansion
  
  # user subshells (...) did this wrong in bash versions before 2.04
  
  ! ( echo hello | grep h >/dev/null 2>&1 ); echo $?
  ! echo hello | grep h >/dev/null 2>&1 ; echo $?
  
  ! true ; echo $?
  ! false; echo $?
  
  ! (false) ; echo $?
  ! (true); echo $?
  
  ! true | false ; echo $?
  ! false | true ; echo $?
  
  ! (true | false) ; echo $?
  ! (false | true) ; echo $?
  