The core identifier of a website (like youtube.com ).
Punycode is a technical standard that allows web browsers to understand and display internet addresses that use non-Latin characters (like Chinese, Japanese, or Arabic). For example, a website with a Japanese name like 日本語.jp is converted by Punycode into xn--wgv71a119e.jp so your browser can locate it. xn video youtube link
A Mozilla support forum thread from September 2021 documented a user experiencing the following error when trying to load a YouTube livestream chatbox: The core identifier of a website (like youtube