edit.check_locs(Editor_state)

  edit.check_locs(Editor_state)

function edit.check_locs(State)
  -- if State is inconsistent (i.e. file changed by some other program),
  --   throw away all cursor state entirely
  if edit.invalid1(State, State.screen_top1)
      or edit.invalid1(State, State.cursor1)
      or not edit.cursor_on_text(State)
      or not Text.le1(State.screen_top1, State.cursor1) then
    State.screen_top1 = {line=1, pos=1}
    edit.put_cursor_on_first_text_line(State)
  end
end

function edit.invalid1(State, loc1)
  return loc1.line > #State.lines
      or loc1.pos > #State.lines[loc1.line].data
end
function edit.cursor_on_text(State)
  return State.cursor1.line <= #State.lines
      and State.lines[State.cursor1.line].mode == 'text'
end
function edit.put_cursor_on_first_text_line(State)
      State.cursor1 = {line=i, pos=1}