def prefix_encode(a, b):
    i = first_diff(a, b)
    return chr(i) + b[i:].encode("utf8")
If drop is targeted into "folder node" (see L{getItemIdInto}), this
dataset/ETHPy150Open tallstreet/Whoosh-AppEngine/src/whoosh/util.py/prefix_encode--crossover with--dataset/ETHPy150Open rwl/muntjac/muntjac/ui/tree.py/TreeTargetDetails.getItemIdAfter