A click on this icon opens the following dialog:
Here you can set borders for the selected text frame, or the
entire text piping chain to which it belongs (for the latter, activate
the checkbox). These borders will be left clear when the text is
formatted. So setting the left border to 2 cm results in the text
starting 2 cm to the right of the left frame edge. These border
settings can be useful in connection with backgrounds to text frames
(see Select frame background
), for example, as you could
otherwise just adapt the frame size and position.
Please note that the border settings may also contain negative values. So a left border set to – 2 cm lets the text protrude 2 cm to the left over the frame's edge.