content: sub error1()
      for i = 0 to 10
          a = i
      end for
      print "a"; a 'error
  end sub
  
  sub error2()
      aa = {}
      if aa <> invalid
          for each a in aa
              b = a
          end for
      end if
      print "b"; b 'error
  end sub
  
  sub ok1()
      a = invalid
      for i = 0 to 10
          a = i
      end for
      print "a"; a
  end sub
  
  sub ok2()
      aa = {}
      b = invalid
      if aa <> invalid
          for each a in aa
              b = a
          end for
      end if
      print "b"; b
  end sub
  