本页总览2.3. Uppercase or Lowercase2.3. Uppercase or Lowercase [RFC4291] does not mention any preference of uppercase or lowercase. 2001:db8:aaaa:bbbb:cccc:dddd:eeee:aaaa2001:db8:aaaa:bbbb:cccc:dddd:eeee:AAAA2001:db8:aaaa:bbbb:cccc:dddd:eeee:AaAa