Changeset [59399] fixed missing DOCTYPEs in normalized HTML output. It missed an edge case where public and system identifiers may contain double quotes, in which case they must be quoted with single quotes.
This commit addresses that issue and adds tests.
Follow-up to [59399].
Reviewed by cbravobernal.
Merges [59410] to the 6.7 branch.
Props jonsurrell, luisherranz, apermo.
Fixes#62396.
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