Switching on (switching off) of mode of vertices insert («Insert»)

If the mode is not made active, at free moving the cursor (without pressing the mouse button), it connects by auxiliary line to the existing point of edited object nearest to them. It means, that it is possible to move (to edit) only existing points of object.

If the mode is made active, at moving the cursor, it connects by auxiliary line to a line of a contour of edited object by the shortest distance, without dependence from presence in this place of really existing point of a contour.

By pressing the left mouse button in a place of a contact of an auxiliary line and a contour of object, the new point is created, which can be moved at once not releasing the mouse button.

Use of a mode probably only for linear and polygon objects.