subrule(?)      # Match one-or-zero times
subrule(s)      # Match one-or-more times
subrule(s?)     # Match zero-or-more times
subrule(N)      # Match exactly N times for integer N > 0
subrule(N..M)   # Match between N and M times
subrule(..M)    # Match between 1 and M times
subrule(N..)    # Match at least N times