Closes #25

tests/README.md

@@ -66,7 +66,7 @@ line numbers for skipped syntax and immediate/deferred errors; warnings precedin
 an error are retained, and failed parses return an empty database. Common headers
 and namespace symbol lists stay quiet. Tests also check file-open errors, fresh
 parse sessions, and compatibility with the legacy throwing API.
-The diagnostic audit also covers 15 unsupported-statement variants, all namespace
+The diagnostic audit also covers 13 unsupported-statement variants, all namespace
 termination forms, CRLF and missing final newlines, relative paths with spaces,
 first-error stopping, deferred diagnostic ordering, duplicate definitions/values,
 selector ranges, overlaps, and preservation of supported decoding and metadata.
@@ -220,3 +220,20 @@ Empty and headers-only fixtures produce an empty runtime database and a valid
 empty tree root. Replacement fixtures change definitions, metadata and decoded
 values, remove old lookup keys, and then clear both outputs through an empty
 fixture. Saved decoded results and trees retain their original metadata.
+
+## Attribute coverage
+
+Parser slots `attributes`, `invalidAttributes`, and `attributeWarnings` cover
+all five scopes and types, deferred definitions/defaults/targets, explicit
+values overriding defaults, repeated assignments, escaped strings, typed
+range/scope errors, duplicate definitions/defaults, unknown attributes and
+missing targets. They check source diagnostics and the throwing API, distinct
+standard/extended targets, frame cycle times and enum labels, unsupported
+formats and ID conflicts, unchanged J1939 opt-in, and runtime/tree propagation.
+Existing unsupported-statement checks now use relation forms, which remain
+unsupported, instead of supported attribute forms.
+
+Attribute changes were verified with `qmake6 ../dbc.pro`, `make -j4`, and
+`make check` in `build/`: all six QtTest suites and the qmake tree target
+passed. The standalone C++17 tree test also passed. The existing named
+comma-decimal C locale test skipped because the locale is not installed.