ID of the YouTube channel of a person or organisation (not to be confused with the name of the channel) The ID can also be used for music.youtube.com IDs.
: Located from the source of the HTML page by searching the source for string: itemprop="channelId" The following command (when replacing CHANNELNAME) can be used on typical Linux distributions to extract the required channel ID to use for this property from a YouTube channel's URL that contains a channel name rather than channel ID: curl --no-progress-meter 'https://www.youtube.com/c/CHANNELNAME' | xmllint --html --recover --nowarning --xpath 'string(//meta[@itemprop="channelId"]/@content)' - 2>/dev/null