You may select an object by clicking it or use a selection-window to select multiple milling lines.
There are two selection modes available.: Replacement and Append selection mode.
You may set the selection mode in de Edit menu.
In the replacement mode each time you do a selection the previous selections will be
unselected unless you hold the Shift key while selecting.
Selecting an already selected milling line, unselects this line.
In the Append mode you can select milling lines by clicking them after each other or use a
selection-window but the previous selections stay selected.
To deselect milling lines, hold the Shift key while clicking on them or you can deselect them
all using the deselect function from the mouse menu or the hot key F2
Holding the Alt key while clicking a milling line, will select the whole milling chain