Official definition of System V service management

[Several](https://danielmiessler.com/study/the-difference-between-system-v-and-systemd/#:~:text=Here%20are%20the%20main%20differences%20between%20the%20two.,much%20more.%20SystemD%20handles%20startup%20processes%20through.service%20files.) [sources](https://fossbytes.com/systemd-vs-sys-v-vs-upstart/) [online](https://www.techtarget.com/searchdatacenter/tip/Master-Linux-service-management-on-System-V-and-systemd) discusses the difference between Linux systemd service management facility and that of System V. While there's an official website for [systemd](https://systemd.io) , I found no official definition for that of System V (I checked SVID issue 2, SVR4's User Manual, Programming Guide, and Sys Admin Guide, and Linux Filesystem Hierarchy Standard). To phrase the question to avoid it being closed as a reference request: Is System V service management facility something officially defined or just a set of conventions adopted by the user community?