零或一个x
x{n,m} n or n+1 or … or m x, prefer more
x{n,} n or more x, prefer more
x{n} exactly n x
x*?...zero or more x, prefer fewer
x+? one or more x, prefer fewer
x?? zero or one x, prefer zero
x{n,m}?...n or n+1 or … or m x, prefer fewer
x{n,}? n or more x, prefer fewer
x{n}?