An edge, or cond-line is selectable through a surface, even if it is hidden behind that surface, if a vertex of that line is visible and that line is part of a primitive.

[nilsschmidt1337]

0. Consider the following test file to display on a 3D view:

0 BFC CERTIFY CCW

1 16 0 0 0 1 0 0 0 1 0 0 0 1 clh1.dat

1. Make sure to disable "View Actions"->"Hidden Vertices". Activate the two-thirds perspective and this mode:
   

2. Double-click on the shown position of clh1.dat to adjust the center of the viewport:
   

3. Click on the position to select the line through the surface:
   

[nilsschmidt1337]

Closed with commit eb7664a.