how to mark object in textdraw(an ascii figure drawer)

[listofx]

hello, everyone
recently, I have drawn a simple figure with ascii art using textdraw.
(sudo apt-get install textdraw; and then run textdraw in a terminal)

for example, I have drawn such a figure:
     end point________________ _________ _________ __________ ____________
       |           |          |         |         |          |
                   |          |         |         |          |
                   |          |         |         |          |
                   |          |         |         |          |
                   |          |         |         |          |
                   |          |         |         |          |
       |____b0_____|__b1______|__b2_____|__b3_____|__b4______|_____________
     start point

the only problem left for me is how to remove(or erase) a object I have
drawn. 
Pressing h will tell us:
d       delete          delete marked object
m       move            move marked object
...(a few lines omiited)
position cursor with cursor keys
mark object at 'hot spot' (<=== the actual meaning?)
to load existing file: <td filename>
try also: home, end, pgdn, pgup

The keypoint is that I could not understand this line:
 mark object at 'hot spot'