diff --git a/src/trio/_core/_parking_lot.py b/src/trio/_core/_parking_lot.py
index ddf6276117..8e2d53ab86 100644
--- a/src/trio/_core/_parking_lot.py
+++ b/src/trio/_core/_parking_lot.py
@@ -146,6 +146,11 @@ class ParkingLot:
     the number of parked tasks, and ``if parking_lot: ...`` to check whether
     there are any parked tasks.
 
+    Attributes:
+        broken_by:
+            The tasks that have broken this lot, in the order in which they
+            did so. Empty as long as the lot is usable; see :meth:`break_lot`.
+
     """
 
     # {task: None}, we just want a deque where we can quickly delete random
diff --git a/src/trio/_subprocess.py b/src/trio/_subprocess.py
index d73ba3dc23..6d2aeaf7a2 100644
--- a/src/trio/_subprocess.py
+++ b/src/trio/_subprocess.py
@@ -98,7 +98,14 @@ def pidfd_open(fd: int, flags: int) -> int:
 class HasFileno(Protocol):
     """Represents any file-like object that has a file descriptor."""
 
-    def fileno(self) -> int: ...
+    def fileno(self) -> int:
+        """Return the file descriptor of the underlying file.
+
+        This is the same method as :meth:`io.IOBase.fileno`, and is what
+        Trio uses to pass the descriptor to the subprocess APIs.
+
+        """
+        ...
 
 
 @final
diff --git a/src/trio/_tests/_check_type_completeness.json b/src/trio/_tests/_check_type_completeness.json
index d8a2948cd9..a44f90dfe0 100644
--- a/src/trio/_tests/_check_type_completeness.json
+++ b/src/trio/_tests/_check_type_completeness.json
@@ -12,7 +12,6 @@
     "all": [
         "No docstring found for class \"trio._core._run.Task\"",
         "No docstring found for class \"trio._socket.SocketType\"",
-        "No docstring found for function \"trio._subprocess.HasFileno.fileno\"",
         "No docstring found for class \"trio._sync.AsyncContextManagerMixin\"",
         "No docstring found for function \"trio._sync._HasAcquireRelease.acquire\"",
         "No docstring found for function \"trio._sync._HasAcquireRelease.release\"",