Will add points on dragged slice line.
|click||add a starting point of a slice line|
|drag||sets end point of slice line|
|drag shift||adjust slice line on x, y or 45°|
|mouse up||slice the glyph according the slice line|
When the slice line has 2 intersection on the same contour it will cut the contour, otherwise is will just add points. (Guides can also slice see Guides)