; https://tools.ietf.org/html/rfc3629#section-4

UTF8-octets = *( UTF8-char )

UTF8-char   = UTF8-1 / UTF8-2 / UTF8-3 / UTF8-4

UTF8-1      = %x00-7F

UTF8-2      = %xC2-DF UTF8-tail

UTF8-3      = %xE0 %xA0-BF UTF8-tail / %xE1-EC 2( UTF8-tail ) /
              %xED %x80-9F UTF8-tail / %xEE-EF 2( UTF8-tail )

UTF8-4      = %xF0 %x90-BF 2( UTF8-tail ) / %xF1-F3 3( UTF8-tail ) /
              %xF4 %x80-8F 2( UTF8-tail )

UTF8-tail   = %x80-BF

