RailwayRouteOptimization/scripts/Snap/SnapAuto/doc/SnapAuto_desc_en.html

<p>The auto snap tool snaps to the closest intersection point, end point,
middle point, perpendicular point, reference point, grid point or point on an
entity in that order of priority.
<br/>
The types of reference points the auto snap tool snaps to can be configured 
under <em>Edit &gt; Application Preferences &gt; Snap &gt; Auto snap</em>.
</p>