When a selection is made using drag&drop (box selection), depending
on the direction the rule for object selection differ:
<ul>
	<li> drag from top-left towards bottom-right (positive sized box):
	     select objects that are fully contained in the box (original behaviour)
	<li> drag in any other direction (e.g. bottom-left to top-right, or
	     bottom-right to top-left; negative sized box):
	     select objects that are even partially within the box or merely touch
	     the edge of the box
</ul>
<p>
As an example, we look at the features in the following layout, which will be
subsequently combined to form a footprint for a B7G thermionic valve. Using a
click and drag selection box going from the top left and then down and
rightwards to the middle of the set of features, as follows: 
<p>
<img src="top-left-down-to-right-selection-box.png">
<p>
we obtain the following selection, namely, only objects that lie entirely
within the selection box, which in this case is only a single pin:
<p>
<img src="top-left-down-to-right-selection-box-resultant-selection.png">
<p>
If we now use a click and drag selection box going from the bottom right
to the middle of the set of features, as follows: 
<p>
<img src="bottom-right-to-up-left-selection-box.png">
<p>
we obtain the following selection, namely, any objects which lie partly
or entirely within the selection box, which includes the silk circle, the
text, the hole and two of the pins:
<p>
<img src="bottom-right-to-up-left-selection-box-resultant-selection.png">
<p>
This feature is of most use on crowded layouts or when selecting from amongst
closely spaced features.
<p>
The feature can be disabled using the editor/selection/disable_negative conf
setting.
<p>
It's possible to limit the feature so that only horizontal-negative is
considered negative size (i.e. only right-to-left dragging), using the
editor/selection/symmetric_negative conf setting.