I understand completely, and the library is intentionally unopinionated in that regard. We simply ensure that the value passed matches the provided schema and ruleset and refine the type in-place.

In certain cases (like validating that an input is ISO8601 format), we refine the input type to a branded type (we have a Iso8601 branded type). At runtime it's just a string, but at compile time TypeScript treats it as a distinct type that can only be obtained through validation. But, it is still not transforming or parsing the data in the way that the blog post intends, which is by design.

https://github.com/nimeshnayaju/valleys?tab=readme-ov-file#i...