Author here. Part 11 of a long series — if this is your first one, part 1 [1] has the setup, and part 5 [2] covers the original GTID_LOG_EVENT which is the natural thing to compare this against.
Honestly, the tagged-GTID feature itself is the less interesting half of this event for me. What caught my attention while researching and writing it is that it's the first binlog event using MySQL's new mysql::serialization framework — a TLV format with field IDs and variants, where optional fields are just absent on the wire and older decoders skip unknown fields by ID. Everything before this was fixed layout (see [2]), so it feels like MySQL is quietly laying groundwork to evolve the binlog format without breaking downstream consumers. Tagged GTIDs are kind of the excuse to ship it.
[1] https://readyset.io/blog/mysql-binary-log-internals-part-1
[2] https://readyset.io/blog/replication-internals-decoding-the-...