    Shift-XX, Ctrl-XX, Alt-XX etc := press key Shift, Ctrl, ... while doing XX
    Mn := Press Mouse Button n
    
    Select node: M1 on node
    Select edge: M1 on edge
    Add node to selection: Shift-M1 on unselected node
    Unselect node: Shift-M1 on selected node
    Unselect edge: Shift-M1 on selected edge

    Move node: M1 on node then drag
    Move selected nodes: M1 on selected node and drag
    Move edge: M1 on edge then drag
    Move edge point: Shift-M1 on edge point then drag

    Add edge point: Select Edge then Shift-Ctrl-M1 on background
    Delete edge point: Select Edge then Shift-Ctrl-M2 near point

    Bring up node menu: M3 on node
    Bring up edge menu: M3 on edge
