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Tests in this virtual suite are running with the CSSArgumentGrammar runtime flag disabled.

The introduction of CSS argument grammar allows certain arbitrary substitution values to be accepted at parse time, even if they are eventually disallowed at computed-value time. This change in behavior causes some existing tests to fail because they expect parse-time rejection. We are waiting for UseCounter results to assess the web-compatibility impact before updating these tests. In the meantime, they are run in this virtual suite with CSSArgumentGrammar disabled to maintain the existing baselines.

See https://drafts.csswg.org/css-values-5/#argument-grammar