var line = new SymbolicConstraint("
    body body1, body2
    vector anchor1, anchor2, direction
    scalar jointMin, jointMax

    limit jointMin (-inf) jointMax
    limit |direction| eps inf

    constraint
        let r1 = relative body1.rotation anchor1 in
        let r2 = relative body2.rotation anchor2 in
        let dir = unit(relative body1.rotation direction) in
        let del = (r2 + body2.position) - (r1 + body1.position) in
        { del cross dir
        del dot dir }

    limit constraint { 0 jointMin } { 0 jointMax }
");