Autogen: Doc: Extend AUTOGEN_TARGET_DEPENDS documentation

Help/prop_tgt/AUTOGEN_TARGET_DEPENDS.rst

@@ -3,15 +3,29 @@ AUTOGEN_TARGET_DEPENDS
 
 Target dependencies of the corresponding ``_autogen`` target.
 
-Targets which have their :prop_tgt:`AUTOMOC` target ``ON`` have a
-corresponding ``_autogen`` target which is used to autogenerate generate moc
-files.  As this ``_autogen`` target is created at generate-time, it is not
-possible to define dependencies of it, such as to create inputs for the ``moc``
-executable.
+Targets which have their :prop_tgt:`AUTOMOC` or :prop_tgt:`AUTOUIC` property
+``ON`` have a corresponding ``_autogen`` target which is used to auto generate
+``moc`` and ``uic`` files.  As this ``_autogen`` target is created at
+generate-time, it is not possible to define dependencies of it,
+such as to create inputs for the ``moc`` or ``uic`` executable.
 
-The ``AUTOGEN_TARGET_DEPENDS`` target property can be set instead to a list of
-dependencies for the ``_autogen`` target.  The buildsystem will be generated to
-depend on its contents.
+The :prop_tgt:`AUTOGEN_TARGET_DEPENDS` target property can be set instead to a
+list of dependencies of the ``_autogen`` target.  Dependencies can be target
+names or file names.
 
 See the :manual:`cmake-qt(7)` manual for more information on using CMake
 with Qt.
+
+Use cases
+^^^^^^^^^
+
+If :prop_tgt:`AUTOMOC` or :prop_tgt:`AUTOUIC` depends on a file that is either
+
+- a :prop_sf:`GENERATED` non C++ file (e.g. a :prop_sf:`GENERATED` ``.json``
+  or ``.ui`` file) or
+- a :prop_sf:`GENERATED` C++ file that isn't recognized by :prop_tgt:`AUTOMOC`
+  and :prop_tgt:`AUTOUIC` because it's skipped by :prop_sf:`SKIP_AUTOMOC`,
+  :prop_sf:`SKIP_AUTOUIC`, :prop_sf:`SKIP_AUTOGEN` or :policy:`CMP0071` or
+- a file that isn't in the target's sources
+
+it must added to :prop_tgt:`AUTOGEN_TARGET_DEPENDS`.