local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
  State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
  Text.clear_screen_line_cache(State, State.cursor1.line)
  State.cursor1.pos = State.cursor1.pos+1

  if State.cursor1.pos then
    local byte_offset = Text.offset(State.lines[State.cursor1.line].data, State.cursor1.pos)
    State.lines[State.cursor1.line].data = string.sub(State.lines[State.cursor1.line].data, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].data, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.pos = State.cursor1.pos+1
  else
    assert(State.cursor1.posB)
    local byte_offset = Text.offset(State.lines[State.cursor1.line].dataB, State.cursor1.posB)
    State.lines[State.cursor1.line].dataB = string.sub(State.lines[State.cursor1.line].dataB, 1, byte_offset-1)..t..string.sub(State.lines[State.cursor1.line].dataB, byte_offset)
    Text.clear_screen_line_cache(State, State.cursor1.line)
    State.cursor1.posB = State.cursor1.posB+1
  end

  State.line_cache[line_index].fragmentsB = nil

  State.line_cache[line_index].screen_line_starting_posB = nil