my token longest_asc_desc {
    # ascending
    | <*0123456789> ** <?after 9>
    | <*1234567890> ** <?after 0>
    | <*2345678901> ** <?after 1>
    ...
    # descending:
    | <*9876543210> ** <?after 0>
    | <*8765432109> ** <?after 9>
    | <*7654321098> ** <?after 8>
    ...
}