[0-9a-z] - base 36 is far from shortest shortener 縮.jp - this one uses utf8 characters and that means their urls won't break 6 characters length for a long lon

[0-9a-z] - base 36 is far from shortest shortener 縮.jp - this one uses utf8 characters and that means their urls won't break 6 characters length for a long long time