deb822 is a newer format to specify system-wide Debian package repositories on Ubuntu in specific fragments (under /etc/apt/sources.list.d/*.sources) and an alternative to sources.list, for which a lexer does already exist. It is supported by APT itself since version 1.1, but lacked support in most of Ubuntu's graphical package management utilities – until Ubuntu decided to remove the sources.list in favour of the new format in the recently released version 24.04. Most tools have since been catching up with the decision, thus it should be quite useful to create a new lexer for the format (technical specification here) and possibly deprecate the sources.list lexer.