[plt-scheme] leading in GUI text

The docs say:

(new text%	 [	[line-spacing line-spacing]	 	 	 	
 	 	[tab-stops tab-stops]	 	 	 	
 	 	[auto-wrap auto-wrap]])	 	→	 	(is-a?/c text%)
  line-spacing : (and/c real? (not/c negative?)) = 1.0
  tab-stops : (listof real?) = null
  auto-wrap : any/c = #f

The line-spacing argument sets the additional amount of space (in DC
units) inserted between each line in the editor when the editor is
displayed. This spacing is included in the reported height of each
line.

The part that I wonder about is "sets the additional amount of space"
Additional to what. In typesetting, leading is just that, the space
between lines. Originally made of lead, hence the name. So what else
is involved and how might one control same. In setting of chess
diagrams, I need the leading to be zero else the diagram will have
nasty little bits of white space.

--hsm