- - - POSSIBLE REVIEW CUTOFF POINT - - -

For the purposes of this refactor, the commits up to this point represent all but one outstanding external-facing change to the `@getodk/xpath` package.

That remaining change will put the project into a temporarily broken state. It has been intentionally held until after this commit, so we can clearly identify where this temporarily broken state begins.

**What's next**

The bulk of the remaining work on this refactor branch involves **integrating** the `@getodk/xpath` changes before this commit into `@getodk/xforms-engine`.

My intent is to keep the aforementioned broken state as short lived as reasonably possible, and to introduce another potential review cutoff when it is resolved.

There will also be a handful of test changes in `@getodk/scenario`. The child-vaccination smoke test's only remaining blocker will be eliminated by this integration work. There is also an open question around select state/itemset filtering (#57) which we've intentionally left broken to keep that question open; some of the integration work necessitates picking one of the options available to answer that question (albeit also temporarily). The select test suite will be updated to reflect that fact, and expanded to more clearly demonstrate the choices available in finally resolving the open question.

Those test changes will likely lag behind the engine integration changes which make them necessary. If I can (relatively) easily identify where these test changes become pertinent, I will try to commit them at the earliest point possible. This will minimize **test/CI breakage** at intermediate commits. But the intent is that, regardless of test/CI state, the project's **user-facing behavior** will continue to work after resolution of the incoming broken state.