About ccTLDs and gTLDs

Hello all,

I am reading RFC1591 and RFC3071 and have a couple of simple questions:
1. Is a ccTLD defined as restricted to 2-letter country codes (ISO3166
alpha 2), or could that include 3-letter country codes in the ISO3166
list (ISO3166 alpha 3)?
2. RFC1591 appears to point at 2-letter, but many other parts of this
RFC are obsolete - so does this RFC remain valid?
Kindest regards,

Olivier

-- 
Olivier MJ Crépin-Leblond, PhD
http://www.gih.com/ocl.html