Clarify some details regarding sys.monitoring

Author: brettcannon

Doc/library/sys.monitoring.rst

@@ -171,7 +171,9 @@ events, use the expression ``PY_RETURN | PY_START``.
       if get_events(DEBUGGER_ID) == NO_EVENTS:
           ...
 
-Events are divided into three groups:
+    Setting this event deactivates all events.
+
+Events can be divided into groups:
 
 .. _monitoring-event-local:
 
@@ -292,9 +294,10 @@ in Python (see :ref:`c-api-monitoring`).
    Activates all the local events for *code* which are set in *event_set*.
    Raises a :exc:`ValueError` if *tool_id* is not in use.
 
-Local events add to global events, but do not mask them.
-In other words, all global events will trigger for a code object,
-regardless of the local events.
+Local events add to global events. In other words, all global events
+will trigger for a code object, regardless of the local events. Events
+will also only trigger once regardless of whether the same event is
+registered both globally and locally for a code object.
 
 
 Disabling events
@@ -325,8 +328,6 @@ except for a few breakpoints.
 Registering callback functions
 ------------------------------
 
-To register a callable for events call
-
 .. function:: register_callback(tool_id: int, event: int, func: Callable | None, /) -> Callable | None
 
    Registers the callable *func* for the *event* with the given *tool_id*
@@ -367,8 +368,15 @@ Different events will provide the callback function with different arguments, as
 
     func(code: CodeType, instruction_offset: int, callable: object, arg0: object | MISSING) -> DISABLE | Any
 
+  *code* represents the code object where the call is being made, while
+  *callable* is the object that is about to be called (and thus
+  triggered the event).
   If there are no arguments, *arg0* is set to :data:`sys.monitoring.MISSING`.
 
+  For instance methods, *callable* will be the function object as found on the
+  class with *arg0* set to the instance (i.e. the ``self`` argument to the
+  method).
+
 * :monitoring-event:`RAISE`, :monitoring-event:`RERAISE`, :monitoring-event:`EXCEPTION_HANDLED`,
   :monitoring-event:`PY_UNWIND`, :monitoring-event:`PY_THROW` and :monitoring-event:`STOP_ITERATION`::