x-refs now has a reference towards the hidden notebook

Author: parmentelat

notebooks/2-05-xrefs-nb.md

@@ -163,3 +163,11 @@ paris_map()
 ### referencing the map
 
 [this should show a map ?](#the-labeled-map)
+
++++
+
+## referencing a hidden notebook
+
+
+
+[Hover me to refer to the cell labeled `the-hidden-reference`](#the-hidden-reference)

notebooks/5-04-hidden-nb.md

@@ -0,0 +1,31 @@
+---
+jupytext:
+  formats: md:myst
+  text_representation:
+    extension: .md
+    format_name: myst
+kernelspec:
+  display_name: Python 3 (ipykernel)
+  language: python
+  name: python3
+language_info:
+  name: python
+  pygments_lexer: ipython3
+  nbconvert_exporter: python
+---
+
+# a hidden notebook
+
++++
+
+this is a hidden notebook with a code cell that has label `the-hidden-reference`
+
+it is referred to from notebook on x-refs
+
+```{code-cell} ipython3
+#| label: the-hidden-reference
+
+# The comment above has special syntax and sets cell metadata.
+# This allows us to embed the output in other places.
+print("Hello world! from the-hidden-reference")
+```