# D010 refinement_violated

URL: /docs/errors/D010
Markdown: /docs/errors/D010.md

> A checked introduction such as Email.from(s) received a value that fails the refinement.

A runtime defect: the running program stops with it; no compile phase reports it, and `try` cannot catch it. `sakura explain D010` prints this explanation offline.

A checked introduction such as `Email.from(s)` received a value that fails the refinement.
Use `validate` (which returns a typed error) at untrusted boundaries.

Runtime defects come from running programs, so `compiler/tests/ui` has no fixture for them; the explanation above names the repair.