IPSocket.valid_v6?

# File tmp/rubies/ruby-3.3.0/lib/ipaddr.rb, line 753
def valid_v6?(addr)
  case addr
  when IPAddr::RE_IPV6ADDRLIKE_FULL
    if $2
      $~[2,4].all? {|i| i.to_i < 256 }
    else
      true
    end
  when IPAddr::RE_IPV6ADDRLIKE_COMPRESSED
    if $4
      addr.count(':') <= 6 && $~[4,4].all? {|i| i.to_i < 256}
    else
      addr.count(':') <= 7
    end
  else
    false
  end
end