Reading-path month: April 2026. Collection published on September 12, 2026. Months organize the reading path; they are not earlier publication dates.
Input validation: valid format does not guarantee meaning
Rules must understand the operation's domain.
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Reading context
A short architecture article. The technical reference supports the topic; hypothetical scenarios and assessment proposals are editorial analysis, not accounts of personal implementations.
Original source ↗The architecture decision
A value can match its expected type while violating a business rule. Validating a date does not establish whether that date is allowed for this transaction.
Practical application
Editorial proposal: separate structural checks from domain conditions. For a hypothetical booking, consider date relationships, booking state and change authorization. Document where the decision is enforced.
How to verify
Ask for formally correct inputs that should be rejected. Discuss ambiguity with product before implementation. Avoid duplicated, inconsistent rules; interface messages help users, but decisions must remain trustworthy when callers use the API directly.