As we continue to improve the ECS tooling, it's sometimes useful to be able to build based on past versions of ECS. Especially when using the ECS tooling to generate customized artifacts.

Backporting the changes to the tooling to past version branches is time intensive and has very small returns, and is therefore unlikely to happen.

Instead we're considering adding the ability to load ECS schema files as of a specific git ref (tag, branch, or commit).

The format of the schema files has been stable enough that I think we'll be able to use this reliably with at least the most recent versions of ECS.