diff --git a/docs/source/conf.py b/docs/source/conf.py
index 925c31e8ef..217927161a 100755
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -172,13 +172,7 @@ def autodoc_process_signature(
 
 # currently undocumented things
 logger = getLogger("trio")
-UNDOCUMENTED = {
-    "trio.MemorySendChannel",
-    "trio.MemoryReceiveChannel",
-    "trio.MemoryChannelStatistics",
-    "trio._subprocess.HasFileno.fileno",
-    "trio.lowlevel.ParkingLot.broken_by",
-}
+UNDOCUMENTED: set[str] = set()
 
 
 def autodoc_process_docstring(
diff --git a/docs/source/reference-lowlevel.rst b/docs/source/reference-lowlevel.rst
index 077f21cd27..315665105d 100644
--- a/docs/source/reference-lowlevel.rst
+++ b/docs/source/reference-lowlevel.rst
@@ -482,6 +482,12 @@ Wait queue abstraction
 .. autoclass:: ParkingLot
    :members:
    :undoc-members:
+   :exclude-members: broken_by
+
+   .. attribute:: broken_by
+
+      The tasks that broke this parking lot. This list is empty until
+      :meth:`break_lot` is called.
 
 .. autoclass:: ParkingLotStatistics
    :members:
diff --git a/newsfragments/3221.doc.rst b/newsfragments/3221.doc.rst
new file mode 100644
index 0000000000..f0a3c0dabc
--- /dev/null
+++ b/newsfragments/3221.doc.rst
@@ -0,0 +1 @@
+Document `MemorySendChannel`, `MemoryReceiveChannel`, and `MemoryChannelStatistics` in the API reference.
diff --git a/src/trio/_channel.py b/src/trio/_channel.py
index 05037d8131..b6b4986f52 100644
--- a/src/trio/_channel.py
+++ b/src/trio/_channel.py
@@ -118,6 +118,26 @@ def __init__(self, max_buffer_size: int | float) -> None:  # noqa: PYI041
 
 @attrs.frozen
 class MemoryChannelStatistics:
+    """Statistics for a memory channel.
+
+    This is returned by `MemorySendChannel.statistics` and
+    `MemoryReceiveChannel.statistics`.
+
+    Attributes:
+      current_buffer_used: The number of values currently stored in the
+          channel buffer.
+      max_buffer_size: The maximum number of values allowed in the buffer, as
+          passed to `open_memory_channel`.
+      open_send_channels: The number of open `MemorySendChannel` endpoints
+          pointing to this channel.
+      open_receive_channels: The number of open `MemoryReceiveChannel`
+          endpoints pointing to this channel.
+      tasks_waiting_send: The number of tasks blocked in
+          `MemorySendChannel.send` on this channel, across all clones.
+      tasks_waiting_receive: The number of tasks blocked in
+          `MemoryReceiveChannel.receive` on this channel, across all clones.
+    """
+
     current_buffer_used: int
     max_buffer_size: int | float
     open_send_channels: int
@@ -152,6 +172,14 @@ def statistics(self) -> MemoryChannelStatistics:
 @final
 @attrs.define(eq=False, repr=False, slots=False)
 class MemorySendChannel(SendChannel[SendType], metaclass=NoPublicConstructor):
+    """The sending side of an in-memory channel.
+
+    A `MemorySendChannel` is created by `open_memory_channel`. Values sent on
+    it are delivered to the matching `MemoryReceiveChannel`. Send channels can
+    be cloned to give multiple producers independent endpoints that all feed
+    the same underlying channel.
+    """
+
     _state: MemoryChannelState[SendType]
     _closed: bool = False
     # This is just the tasks waiting on *this* object. As compared to
@@ -300,6 +328,14 @@ async def aclose(self) -> None:
 @final
 @attrs.define(eq=False, repr=False, slots=False)
 class MemoryReceiveChannel(ReceiveChannel[ReceiveType], metaclass=NoPublicConstructor):
+    """The receiving side of an in-memory channel.
+
+    A `MemoryReceiveChannel` is created by `open_memory_channel`. It receives
+    values from the matching `MemorySendChannel`. Receive channels can be
+    cloned to give multiple consumers independent endpoints that share the
+    same underlying channel.
+    """
+
     _state: MemoryChannelState[ReceiveType]
     _closed: bool = False
     _tasks: set[trio._core._run.Task] = attrs.Factory(set)
diff --git a/src/trio/_subprocess.py b/src/trio/_subprocess.py
index d73ba3dc23..7b5293d8e2 100644
--- a/src/trio/_subprocess.py
+++ b/src/trio/_subprocess.py
@@ -98,7 +98,9 @@ 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 integer file descriptor for this object."""
+        ...
 
 
 @final
diff --git a/src/trio/_tests/_check_type_completeness.json b/src/trio/_tests/_check_type_completeness.json
index 6e8c54ea8b..309b4e13f3 100644
--- a/src/trio/_tests/_check_type_completeness.json
+++ b/src/trio/_tests/_check_type_completeness.json
@@ -18,12 +18,6 @@
     ],
     "Windows": [],
     "all": [
-        "No docstring found for class \"trio.MemoryReceiveChannel\"",
-        "No docstring found for class \"trio._channel.MemoryReceiveChannel\"",
-        "No docstring found for class \"trio.MemoryChannelStatistics\"",
-        "No docstring found for class \"trio._channel.MemoryChannelStatistics\"",
-        "No docstring found for class \"trio.MemorySendChannel\"",
-        "No docstring found for class \"trio._channel.MemorySendChannel\"",
         "No docstring found for class \"trio._core._run.Task\"",
         "No docstring found for class \"trio._socket.SocketType\"",
         "No docstring found for function \"trio._highlevel_socket.SocketStream.send_all\"",
@@ -31,7 +25,6 @@
         "No docstring found for function \"trio._highlevel_socket.SocketStream.send_eof\"",
         "No docstring found for function \"trio._highlevel_socket.SocketStream.receive_some\"",
         "No docstring found for function \"trio._highlevel_socket.SocketStream.aclose\"",
-        "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\"",