button = left, middle, right, wheel, double_left, double_middle, double_right, single_left, single_middle, or single_right
modifiers = None, Shft, Ctrl, CtSh, CtAl, CtAl, CtAS,
actions = None, Rota, Move, MovZ, Slab, +Box, -Box, Clip, MovS, +/-, PkAt, Pk1, MvSZ, Sele, Orig, Menu, PkAt, Pk1 RotO, MovO, MvOZ, MovA, PkAt, PkTB, MvSZ MvAZ, DrgM, RotZ, PkBd, ClpN, ClpF
jymol.cmd.button("left", "none", "box")
will set the function of the left button when no modifiers are pressed to selection by rectangular area.