diff --git a/docs/database.md b/docs/database.md
index 96e9a3c..5b2cb58 100644
--- a/docs/database.md
+++ b/docs/database.md
@@ -212,9 +212,10 @@ def resolve_user_key(value: str) -> str | None:
 
 - By default a transaction is logged with an `action by user` header followed
   by the diff lines.  Added paths are colored green, deleted paths red.
-- `kanta.transaction(..., extra="...")` accepts a display-only string that is
-  appended after the action in the header (colored by Kanta); it is never
-  persisted in the `ChangeRecord`.
+- `kanta.transaction(..., extra=...)` accepts a display-only value that is
+  shown after the action in the header.  Anything other than `None` is
+  printed str-converted (colored by Kanta), unless a custom logemit handler
+  does something else with it; it is never persisted in the `ChangeRecord`.
 - `kanta.transaction(..., logdiff=False)` skips building and printing the diff
   body and logs only the header, which is useful for large or noisy
   changesets.  Diff output can also be disabled globally with
diff --git a/kanta/kanta.py b/kanta/kanta.py
index 9422977..6eca545 100644
--- a/kanta/kanta.py
+++ b/kanta/kanta.py
@@ -5,7 +5,7 @@ import logging
 from datetime import datetime
 from pathlib import Path
 from types import ModuleType, SimpleNamespace
-from typing import Generic, TypeVar
+from typing import Any, Generic, TypeVar
 
 from kanta.kantaimpl import KantaImpl
 from kanta.serialization import JsonSerializer, Serializer
@@ -345,7 +345,7 @@ class Kanta(Generic[T]):
         action: str,
         *,
         user: str | None = None,
-        extra: str | None = None,
+        extra: Any = None,
         mtime: bool | datetime = True,
         log: bool | logging.Logger = True,
         logdiff: bool = True,
@@ -357,9 +357,11 @@ class Kanta(Generic[T]):
             user: Optional user identifier stored in metadata and rendered in
                 the log header.  Register a ``@kanta.logfmt`` callback to format
                 the user value; the path ``"$user"`` is passed for this case.
-            extra: Optional display-only string appended after the action in
-                the log header (colored by Kanta).  It is never persisted in
-                the change record.
+            extra: Optional display-only value shown after the action in the
+                log header.  Anything other than ``None`` is printed
+                str-converted (colored by Kanta), unless a custom
+                ``@kanta.logemit`` handler does something else with it.  It is
+                never persisted in the change record.
             mtime: Controls the modification time ``m``. ``True`` (default)
                 sets ``m`` to the current UTC time. ``False`` omits ``m`` so the
                 previous modification time remains in effect; this is used for
diff --git a/kanta/logging.py b/kanta/logging.py
index 094440d..910ea26 100644
--- a/kanta/logging.py
+++ b/kanta/logging.py
@@ -55,7 +55,7 @@ class LogEvent(msgspec.Struct, kw_only=True):
     kanta: Any = None
     action: str | None = None
     user: str | None = None
-    extra: str | None = None
+    extra: Any = None
     error: BaseException | None = None
     diff: dict = msgspec.field(default_factory=dict)
     previous: dict | None = None
@@ -413,13 +413,13 @@ def format_diff(
 def format_action_header(
     action: str,
     user: str | None = None,
-    extra: str | None = None,
+    extra: Any = None,
 ) -> str:
     """Format the default action header line."""
     line = Line().action(action)
-    if extra:
+    if extra is not None and (extra := f"{extra}"):
         line(" ").target(extra)
-    if user:
+    if user is not None and (user := f"{user}"):
         line(" by ").user(user)
     return str(line)
 
@@ -429,7 +429,7 @@ def log_change(
     diff: dict,
     user: str | None = None,
     previous: dict | None = None,
-    extra: str | None = None,
+    extra: Any = None,
     logfmt: Callable[[Any, str], str | None] | None = None,
     *,
     logger: logging.Logger = transaction_logger,
@@ -447,8 +447,10 @@ def log_change(
         diff: The JSON diff dict.
         user: Optional already-formatted user name to show in the header.
         previous: The previous state dict (for determining add vs update).
-        extra: Optional display-only string appended after the action in the
-            header (colored by Kanta).
+        extra: Optional display-only value shown after the action in the
+            header.  Anything other than ``None`` is printed str-converted
+            (colored by Kanta), unless a custom logemit handler does
+            something else with it.
         logfmt: Optional formatter callable ``(value, path) -> str | None``.
         logger: Logger to write to. Defaults to the ``kanta.transaction`` logger.
         level: Log level to use. Defaults to ``logging.INFO``.
diff --git a/kanta/transaction.py b/kanta/transaction.py
index 0f44cae..bea48a5 100644
--- a/kanta/transaction.py
+++ b/kanta/transaction.py
@@ -5,6 +5,7 @@ from __future__ import annotations
 import logging
 from contextlib import contextmanager
 from datetime import datetime
+from typing import Any
 
 from kanta.diff import compute_diff
 from kanta.exceptions import DataIntegrityError
@@ -40,7 +41,7 @@ def transaction(
     action: str,
     *,
     user: str | None = None,
-    extra: str | None = None,
+    extra: Any = None,
     mtime: bool | datetime = True,
     log: bool | logging.Logger = True,
     logdiff: bool = True,