Update __init__.py

Author: Tom-van-Woudenberg

sphinx_external_toc/__init__.py

@@ -31,6 +31,13 @@ def setup(app: "Sphinx") -> dict:
     # variables
     app.add_config_value("external_toc_path", "_toc.yml", "env")
     app.add_config_value("external_toc_exclude_missing", False, "env")
+    
+    # Register use_multitoc_numbering if not already registered (e.g., by JupyterBook)
+    try:
+        app.add_config_value("use_multitoc_numbering", True, "env")
+    except Exception:
+        # Already registered, likely by JupyterBook
+        pass
 
     # Note: this needs to occur after merge_source_suffix event (priority 800)
     # this cannot be a builder-inited event, since if we change the master_doc