[Docutils-develop] [docutils:bugs] #511 Problems with nested parsing and sections.

The remaining issue is a way to tell `RSTState.nested_parse()` that it shall use a new, separate title style hierarchy for section headings (similar to Sphinx `nested_parse_to_nodes()`).


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**[bugs:#511] Problems with nested parsing and sections.**

**Status:** pending-remind
**Created:** Tue Aug 26, 2025 10:13 AM UTC by Günter Milde
**Last Updated:** Sat Sep 13, 2025 08:31 AM UTC
**Owner:** nobody
**Attachments:**

- [old_nested_parsing.py](https://sourceforge.net/p/docutils/bugs/511/attachment/old_nested_parsing.py) (7.5 kB; text/x-python)


In Docutils <= 0.22, parsing a nested content block with `docutils.parsers.rst.state.RSTState.nested_parse()` uses the document-wide "title style hierarchy".

With Docutils <=0.21, this method can **loose complete sections** without warning when the `match_titles` argument is True and the nested content block contains sections with a title style that matches a lower section level than the current section level (try the attached test with a Docutils version below 0.22).

Docutils itself does not use `nested_parse()` with `match_titles` True and did not test.
However, the feature is used by Sphinx and several Sphinx extensions (cf. [bugs:#508], [bugs:#509], and  https://github.com/sphinx-doc/sphinx/issues/13845).

The new section parsing algorithm introduced in Docutils 0.22 fixes the data loss, but  sections with a title style that matches a lower section level than the current section level are attached in wrong order: After the nested parsing is complete, the calling parser continues where it left of, messing the order of elements in the doctree (try the attached test with [r10204]).

This was fixed in [r10206] at the expense of dropping support for document-wide title styles in nested parsing. 
As a result, the Sphinx "only" directive (which uses a new section style hierarchy with later re-attachment of the first section) now fails: https://github.com/sphinx-doc/sphinx/issues/13861


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