Add tests for DOCTYPE system identifier empty vs missing distinction #57077
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This adds tests to verify that an empty DOCTYPE system identifier is treated the same as a missing one for quirks mode determination, aligning with Chromium and WebKit behavior. Tests: - Frameset/Transitional + empty system ID → quirks mode - Frameset/Transitional + missing system ID → quirks mode - Frameset/Transitional + non-empty system ID → limited-quirks mode See whatwg/html#12023
zcorpan
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Jan 9, 2026
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Looks good, but the spec should be changed before landing.
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This PR adds tests to verify the behavior of DOCTYPE system identifier handling for quirks mode determination.
Related Issue
Summary
The HTML spec currently distinguishes between a missing system identifier and an empty string (
"") system identifier. However, Chromium and WebKit treat both cases identically (as quirks mode triggers).Test Cases
compatMode-//W3C//DTD HTML 4.01 Frameset//""(empty)BackCompat-//W3C//DTD HTML 4.01 Frameset//BackCompat-//W3C//DTD HTML 4.01 Frameset//CSS1Compat-//W3C//DTD HTML 4.01 Transitional//""(empty)BackCompat-//W3C//DTD HTML 4.01 Transitional//BackCompat-//W3C//DTD HTML 4.01 Transitional//CSS1CompatExpected Results
Test Results Screenshots
Chrome
Safari
Firefox
Files Added
html/syntax/parsing/doctype-system-identifier-distinction.html- Main test filehtml/syntax/parsing/support/doctype-system-id-empty-frameset.htmlhtml/syntax/parsing/support/doctype-system-id-empty-transitional.htmlhtml/syntax/parsing/support/doctype-system-id-missing-frameset.htmlhtml/syntax/parsing/support/doctype-system-id-missing-transitional.htmlhtml/syntax/parsing/support/doctype-system-id-nonempty-frameset.htmlhtml/syntax/parsing/support/doctype-system-id-nonempty-transitional.html