some content for local testing of xrefs

Author: stevejpurves

content/external.md

@@ -7,8 +7,46 @@ MyST Supports cross-referencing into external content in order to create figures
 
 ![](xref:guide#img:altair-horsepower)
 
-
 ## An External Embed!
 
 :::{embed} xref:guide#img:altair-horsepower
-:::
+:::
+
+# Local testing
+
+::::{tip} On local testing
+:class: dropdown
+
+
+1. get test source content in `folderA`
+  * myst start --execute --headless
+  * content server running on `localhost:3100`
+2. start myst-theme e.g. `npm run theme:book`
+  * theme running on `localhost:3000`
+3. get second set of test content in `folderB`
+  * add `local: http://localhost:3000` to `myst.yml#project.references`
+  * add external cross references and embeds in `folderB` pointing to the local content in `folderA`
+  * `myst start --execute --headless`
+  * content server running on `localhost:3101`
+4. in a second `myst-theme` folder, or without fully restarting the theme from step 2
+  * add a `.env` file to `themes/book`
+  * add `CONTENT_CDN_PORT=3101`
+  * `npm run theme:book`
+  * theme running on `localhost:3001`
+  * test this website 👆
+
+::::
+
+## A local embed (shorthand)
+
+![](xref:local#out:simple-matplotlib)
+
+## a local embed
+
+:::{embed} xref:local#out:simple-matplotlib
+:::
+
+## cross references
+
+* [To a notebook cell](xref:local#out:simple-matplotlib)
+* [To a figure](xref:local#fig:simple-matplotlib)

myst.yml

@@ -5,6 +5,7 @@ project:
   title: Jupyter Outputs
   references:
     guide: https://mystmd.org/guide
+    # local: http://localhost:3000
   toc:
     - file: content/summary.md
     - file: content/testing.md