docs: extra hooks functions and utilities

docs/reference/api/hooks/index.rst

@@ -1,8 +1,11 @@
 .. _hooks_api:
 
-==========
-Hook types
-==========
+=========
+Hooks API
+=========
+
+Types
+=====
 
 This is the Python documentation of the two types of hooks (actions and filters) as well as the contexts system which is used to instrument them. Understanding how Tutor hooks work is useful to create plugins that modify the behaviour of Tutor. However, plugin developers should almost certainly not import these hook types directly. Instead, use the reference :ref:`hooks catalog <hooks_catalog>`.
 
@@ -12,3 +15,17 @@ This is the Python documentation of the two types of hooks (actions and filters)
    actions
    filters
    contexts
+
+Utilities
+=========
+
+Functions
+---------
+
+.. autofunction:: tutor.core.hooks::clear_all
+
+Priorities
+----------
+
+.. automodule:: tutor.core.hooks.priorities
+   :members: HIGH, DEFAULT, LOW

tutor/core/hooks/priorities.py

@@ -4,8 +4,12 @@ import typing as t
 
 from typing_extensions import Protocol
 
+#: High priority callbacks are triggered first.
 HIGH = 5
+#: By default, all callbacks have the same priority and are processed in the order they
+#: were added.
 DEFAULT = 10
+#: Low-priority callbacks are called last. Add callbacks with this priority to override previous callbacks. To add callbacks with even lower priority, use ``LOW + somevalue`` (though such behaviour is not encouraged).
 LOW = 50