[ZFzuofeng]

Description

Document existing attribute-combination behavior without changing runtime behavior. The example combines source-name lists without modifying the inputs, and gives consistent results when combination happens in stages. Also clarify that compat="identical" checks attributes even with combine_attrs="drop".

Related to #6679.

Validation

• Related merge/concat/combine tests: 355 passed, 1 existing xfailed.
• Executed the affected guide in a real Jupyter kernel: 30 cells, including one explicitly expected MergeError.
• Isolated Sphinx build with warnings treated as errors, rendered example/navigation/API-link checks, Prettier, blackdoc, and git diff --check passed.
• The final prose-only clarification was rechecked through execution, rendering, links, and formatting; the unchanged related tests were not repeated afterward.

The example handles source names stored as lists of strings; it is not a general attribute-merging policy. The full documentation site, full test suite, and complete pre-commit suite were not run locally.

Checklist

• Documentation example executed and checked.

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR. Tools: OpenAI Codex, used to review and verify the supplied candidate, revise the documentation, and translate the submitter's Chinese explanation.
    Prompt scope: review the supplied contribution candidates, explain their changes and limitations, and submit after human review.

The human submitter reviewed the changes and stated, in Chinese, that this documents existing behavior, accepts the described limitations, and takes responsibility for the contribution. The explanation above translates that reviewed rationale; validation results are recorded from the local runs.

[This is OpenAI Codex submitting on behalf of @ZFzuofeng, after their review and explicit authorization.]