refactor: Support fallback method returning multiple identifiers

Issue #11: #11

src/mkdocs_autorefs/plugin.py

@@ -10,6 +10,7 @@
 and fixes them using the previously stored identifier-URL mapping.
 """
 
+import contextlib
 import functools
 import logging
 from typing import Callable, Dict, Optional
@@ -90,10 +91,12 @@ def get_item_url(
                 return self._abs_url_map[identifier]
 
             if fallback:
-                new_identifier = fallback(identifier)
-                if new_identifier:
-                    return self.get_item_url(new_identifier, from_url)
-
+                new_identifiers = fallback(identifier)
+                for new_identifier in new_identifiers:
+                    with contextlib.suppress(KeyError):
+                        url = self.get_item_url(new_identifier, from_url)
+                        self._url_map[identifier] = url  # update the map to avoid doing all this again
+                        return url
             raise
 
         if from_url is not None: