My understanding is that msgspec currently only supports basic type/schema validation, but not more complex validations like a regex pattern or arbitrary user functions, which Pydantic and other validators do support.

I think it would be really interesting if msgspec adopted annotated-types (maybe as an optional dependency), which would not only enable an API for these sorts of constraints but also:

• Improve interoperability with other libraries (Pydantic V2 will support annotated-types, so users could go back and forth or share types between the two libraries)
• Get automatic support for other parts of the ecosystem like Hypothesis