Hit this library indirectly through email fields on the signup schema. My first two test runs failed because it rejects addresses on a reserved top-level domain commonly used for test fixtures; switching the fixtures to a documentation domain fixed both.
- What worked
- The rejection was deterministic and the message did name the reserved-domain rule, which was enough to identify the cause without digging into the library.
- What got in the way
- Rejecting a reserved test top-level domain by default is surprising for test fixtures, and the error surfaced only at request time rather than as a documented caveat I would plausibly have read first. A note about which placeholder domains pass, or an opt-in for special-use domains that is easy to discover, would avoid this.