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Add tests for DOCTYPE system identifier empty vs missing distinction #57077

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Merged
zcorpan merged 1 commit into from
Jan 14, 2026
Merged

Add tests for DOCTYPE system identifier empty vs missing distinction #57077

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82 changes: 82 additions & 0 deletions html/syntax/parsing/doctype-system-identifier-distinction.html
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<!DOCTYPE html>
<meta charset="utf-8" />
<title>DOCTYPE system identifier: empty string treated as missing</title>
<link
rel="help"
href="https://html.spec.whatwg.org/multipage/parsing.html#the-initial-insertion-mode"
/>
<link rel="help" href="https://github.com/whatwg/html/issues/12023" />
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
// Tests that an empty string system identifier is treated the same as a missing
// system identifier for quirks mode determination.
// See https://github.com/whatwg/html/issues/12023
//
// The important distinction that must be preserved:
// - missing system ID → quirks mode (BackCompat)
// - empty system ID → quirks mode (BackCompat) [same as missing]
// - non-empty system ID → limited-quirks mode (CSS1Compat) [different from missing]

const testCases = [
// HTML 4.01 Frameset - empty system ID (treated same as missing)
{
file: "support/doctype-system-id-empty-frameset.html",
expected: "BackCompat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Frameset//" and empty system ID triggers quirks mode',
},
// HTML 4.01 Frameset - missing system ID
{
file: "support/doctype-system-id-missing-frameset.html",
expected: "BackCompat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Frameset//" and missing system ID triggers quirks mode',
},
// HTML 4.01 Frameset - non-empty system ID (must remain different!)
{
file: "support/doctype-system-id-nonempty-frameset.html",
expected: "CSS1Compat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Frameset//" and non-empty system ID triggers limited-quirks mode',
},
// HTML 4.01 Transitional - empty system ID (treated same as missing)
{
file: "support/doctype-system-id-empty-transitional.html",
expected: "BackCompat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Transitional//" and empty system ID triggers quirks mode',
},
// HTML 4.01 Transitional - missing system ID
{
file: "support/doctype-system-id-missing-transitional.html",
expected: "BackCompat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Transitional//" and missing system ID triggers quirks mode',
},
// HTML 4.01 Transitional - non-empty system ID (must remain different!)
{
file: "support/doctype-system-id-nonempty-transitional.html",
expected: "CSS1Compat",
description:
'DOCTYPE with "-//W3C//DTD HTML 4.01 Transitional//" and non-empty system ID triggers limited-quirks mode',
},
];

for (const testCase of testCases) {
async_test((t) => {
const iframe = document.createElement("iframe");
iframe.onload = t.step_func_done(() => {
assert_equals(
iframe.contentDocument.compatMode,
testCase.expected,
`compatMode should be ${testCase.expected}`
);
iframe.remove();
});
iframe.src = testCase.file;
document.body.appendChild(iframe);
}, testCase.description);
}
</script>
3 changes: 3 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-empty-frameset.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//" "">
<meta charset="utf-8" />
<title>DOCTYPE with empty system identifier (Frameset)</title>
4 changes: 4 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-empty-transitional.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//" "">
<meta charset="utf-8">
<title>DOCTYPE with empty system identifier (Transitional)</title>

4 changes: 4 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-missing-frameset.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//">
<meta charset="utf-8">
<title>DOCTYPE with missing system identifier (Frameset)</title>

4 changes: 4 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-missing-transitional.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//">
<meta charset="utf-8">
<title>DOCTYPE with missing system identifier (Transitional)</title>

4 changes: 4 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-nonempty-frameset.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Frameset//" "http://www.w3.org/TR/html4/frameset.dtd">
<meta charset="utf-8">
<title>DOCTYPE with non-empty system identifier (Frameset)</title>

4 changes: 4 additions & 0 deletions html/syntax/parsing/support/doctype-system-id-nonempty-transitional.html
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//" "http://www.w3.org/TR/html4/loose.dtd">
<meta charset="utf-8">
<title>DOCTYPE with non-empty system identifier (Transitional)</title>