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Expand Qt XML documentation on behavior changes in Qt 6

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Adds a more detailed overview of behavior changes between Qt 5 and Qt 6
in the Qt XML module. This update is based on multiple reported tickets
highlighting behavior differences, where users requested further
explanations.

Fixes: QTBUG-134503
Pick-to: 6.9 6.8
Change-Id: I2e25268c6de7fd7e3a0e0244b83bb2ba616ef60e
Reviewed-by: Safiyyah Moosa <safiyyah.moosa@qt.io>
Reviewed-by: Mate Barany <mate.barany@qt.io>
This commit is contained in:
Magdalena Stojek 2025-03-10 12:32:00 +01:00
parent 7bec2f6b42
commit 275396b013
1 changed files with 43 additions and 5 deletions
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48
src/xml/doc/src/qt6-changes.qdoc
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@ -12,7 +12,18 @@
We try to maintain binary and source compatibility for all the public
APIs in each release. But some changes were inevitable in an effort to
make Qt a better framework.
make Qt a better framework and align with modern standards.
Qt 6 enforces XML 1.0 rules more strictly than Qt 5. In Qt 5,the XML
parser was more lenient, allowing certain constructs that were not
compliant with the XML 1.0 specification.
Qt 6 corrects this behavior, ensuring that XML handling follows
the standard properly. If your application relies on behavior
that was incorrectly permitted in Qt 5, you may need to adjust your
XML documents or processing logic accordingly.
For more details on XML 1.0 rules, see the official W3C XML specification:
\l {https://www.w3.org/TR/xml/} {Extensible Markup Language (XML) 1.0 (Fifth Edition)}
In this topic we summarize those changes in Qt XML, and provide
guidance to handle them.
@ -70,10 +81,34 @@
\li Undeclared namespace prefixes are no longer allowed.
\endlist
If you use QDomDocument and rely on any of these, you must update
your code and XML documents accordingly.
For more details see:
\l {https://www.w3.org/TR/xml/#AVNormalize} {Attribute-Value Normalization in XML 1.0}
\section3 Spacing-only text nodes
\section2 Control characters
In Qt 6, control characters such as U+0000—U+001F, U+007F, and U+0080—U+009F
are now correctly rejected per XML 1.0 rules.
They were incorrectly allowed in Qt 5.
Before using XML with Qt6 ensure that your XML documents contain only valid
XML 1.0-compliant characters. If control characters are necessary, encode
them using text-safe format.
For more details see:
\l {https://www.w3.org/TR/xml/#charsets} {Characters in XML 1.0}
\section2 HTML Entities in XML
In Qt 6, HTML entities are no longer valid unless explicitly declared in a
Document Type Definition (DTD). In Qt 5, certain HTML-specific entities
(e.g., \c{&nbsp;}) were allowed, even without declaration. To ensure
compatibility in Qt 6 use numeric character references, define required
entities in a DTD or if your content relies on HTML entities, process
the XML as HTML instead.
For more details see:
\l {https://www.w3.org/TR/xml/#charencoding} {Character Encoding in Entities in XML 1.0}
\section2 Spacing-only text nodes
By default, text nodes containing only spacing characters are stripped
and won't appear in the QDomDocument. The Qt 5 way of changing this behavior
@ -82,7 +117,10 @@
you can pass QDomDocument::ParseOption::PreserveSpacingOnlyNodes as a parse
option, to specify that spacing-only text nodes must be preserved.
\section2 Qt Core5 compatibility library
If you use QDomDocument and rely on any of these, you must update
your code and XML documents accordingly.
\section1 Qt Core5 compatibility library
If your application or library cannot be ported right now, the \l
QXmlSimpleReader and related classes still exist in Qt5Compat to keep