Clicking on a line should locate the appropriate reply (not implemented here). In the example, a click on the first line should go to Reply2. Second line, to Reply12, Third line, to Reply11. Fourth line, to Reply2. Fifth line, to Reply 1.

(Clicking on a line with a down arrow should locate the next sibling of the reply above the line. If there is no next sibling, the next reply at a higher level should be located. If there is neither, the line should be drawn, but no action taken on click. Clicking on a line with an up arrow should locate the previous sibling of the reply below the line.)