TLD/gTLDについて、ここに記述してください。
https://www.icann.org/resources/board-material/resolutions-2016-11-08-en#2.a
registry operators to reserve two-character ASCII labels within the TLD at the second level.
“The GAC recognized that two-character second level domain names are in wide use across existing TLDs, and have not been the cause of any security, stability, technical or competition concerns. The GAC is not in a position to offer consensus advice on the use of two-character second level domains names in new gTLD registry operations, including those combinations of letters that are also on the ISO 3166-1 alpha 2 list.”