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[patch] Require the 978/979 Bookland prefix on an ISBN-13 - #407
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IsIsbnAttribute only checked an ISBN-13's mod-10 check digit, which every
EAN-13 barcode passes, so Isbn.Create("4006381333931") accepted a non-book
product code. An ISBN-13 must now start with 978 or 979.
Fixes #334
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LoEzLXruuTHCcJnXtVa49Z
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This was referenced Oct 9, 2026
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Fixes #334
What was wrong
IsIsbnAttributechecked only an ISBN-13's mod-10 check digit. Every EAN-13 barcode passes that check, soIsbn.Create("4006381333931"), a non-book product code, validated as an ISBN.Change (
Semantics.Strings.Identifiers)IsIsbnAttribute.IsValidIsbn13rejects any value that doesn't start with978or979, the Bookland range ISBNs are allocated from. It runs before the checksum.IsIsbnAttributeandIsbnand the rules table in the package README now mention the prefix.Release note: this tightens validation. An
Isbnthat was stored from a non-978/979 EAN-13 will now failCreateandTryCreate.Tests (
IsbnTests)Create_Ean13OutsideBooklandRange_Throws:4006381333931(the issue's example),5901234123457, and9770317847001(an ISSN-style977barcode). Each has a valid EAN-13 check digit and now throwsArgumentException.TryCreate_Ean13OutsideBooklandRange_ReturnsFalse:TryCreatereturnsfalsewith a null result.Create_ValidIsbn13With979Prefix_Succeeds:979-10-90636-07-1still validates, so the979range keeps working.Verification
IsIsbnAttribute.csreverted, the 4 out-of-range cases fail. With the fix, all 12IsbnTestspass.Semantics.Testsuite passes on net10.0: 1485 passed, 0 failed, 8 skipped (the same 8 are skipped onmain).Semantics.Strings.Identifiersbuilds with the local Sonar analyzers (.sonarlint/sonar-local.props) with 0 warnings.🤖 Generated with Claude Code
https://claude.ai/code/session_01LoEzLXruuTHCcJnXtVa49Z
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