Merge pull request #1412 from quarto-dev/sync-1411-to-prerelease

[Sync to prerelease] Add callout for unique footnote IDs

docs/authoring/markdown-basics.qmd

@@ -210,6 +210,16 @@ This syntax generates the following output:
 Here is an inline note.[^3]
 :::
 
+::: {.callout-note}
+
+## Footnote IDs should be unique
+
+Footnote identifiers, e.g., the `1` in `^1`, need to be unique within a document. 
+In Quarto books, chapters are combined into a single document for certain formats (including PDF, DOCX, and EPUB),
+so footnote identifiers need to be unique **across** chapters. 
+
+:::
+
 The footnotes that are generated from the above examples are included in the [Example Footnotes](#example-footnotes) section at the bottom of the page. See the [Pandoc Footnotes](https://pandoc.org/MANUAL.html#footnotes) for additional information.
 
 [^1]: Here is the footnote.