Pfx.teredo-question-mark
You're seeing just the function
teredo-question-mark, go back to Pfx module for more information.
Specs
Returns true if given pfx is a teredo address, false otherwise
IPv6 address within the teredo service prefix of 2000:0::/32
More details in rfc4380.
Examples
iex> teredo?("2001:0000:4136:e378:8000:63bf:3fff:fdd2")
true
iex> teredo?("1.1.1.1")
false
iex> teredo?(42)
false