# File lib/sup/modes/thread-view-mode.rb, line 316
  def activate_chunk
    chunk = @chunk_lines[curpos] or return
    if chunk.is_a? Chunk::Text
      ## if the cursor is over a text region, expand/collapse the
      ## entire message
      chunk = @message_lines[curpos]
    end
    layout = if chunk.is_a?(Message)
      @layout[chunk]
    elsif chunk.expandable?
      @chunk_layout[chunk]
    end
    if layout
      layout.state = (layout.state != :closed ? :closed : :open)
      #cursor_down if layout.state == :closed # too annoying
      update
    elsif chunk.viewable?
      view chunk
    end
    if chunk.is_a?(Message)
      jump_to_message chunk
      jump_to_next_open if layout.state == :closed
    end
  end