What are the semantics of `patch()`?

It seems that `patch` won't _augment_ existing objects: e.g. if I patch a list with a larger list, the patchee won't get any push for the missing entries. Ditto for structs, and there it makes sense imo: while we could _add new fields_ to the reflected value, this wouldn't have any effect when converting back to the actual struct type. At the same time, one could use `Value` as a very generic way to manipulate values in general, and then it might make sense to add new fields etc (e.g. a serialization framework could use that to run "migrations").

I'm not advocating for one way or another, I'm just curious about the _why_ behind this choice, and I think it'd make sense documenting that choice in a doc-comment on `patch()` :)

Locate the implementation and existing documentation for `patch()` first. Check how patching behaves for lists and structs, then document those semantics and the rationale in the `patch()` doc-comment. Done means the comment explains whether missing entries or fields are augmented and why.

Written by the indexing model from the issue text.