Conceptual guides and component architecture fix

docs/backend/subscribers.md

@@ -1,14 +1,12 @@
 ---
 myst:
   html_meta:
-    "description": "How to add custom event handlers for your type in Plone"
-    "property=og:description": "How to add custom event handlers for your type in Plone"
+    "description": "How to register and use event subscribers in Plone"
+    "property=og:description": "How to register and use event subscribers in Plone"
     "property=og:title": "Subscribers (event handlers)"
-    "keywords": "Plone, subscribers, event handlers"
+    "keywords": "Plone, events, subscribers, event handlers, ZCA"
 ---
 
-(backend-subscribers-label)=
-
 # Subscribers (event handlers)
 
 A _subscriber_ is a callable object that takes one argument, an object that we call the _event_.
@@ -18,72 +16,70 @@ They are used to extend processing by providing processing plug points.
 
 A _notification_ alerts subscribers that an event has occurred.
 
-The {term}`Zope Component Architecture`'s [`zope.event`](https://zopeevent.readthedocs.io/en/latest/) package is used to manage subscribable events in Plone.
+The Zope Component Architecture's zope.event package is used to manage subscribable events in Plone.
 
 The Plone event system has some notable characteristics:
 
--   It's simple.
--   The calling order of subscribers is random.
-    You can't set the order in which event handlers are called.
--   Events can't be cancelled.
-    All handlers will always get the event.
--   Event handlers can't have return values.
--   Exceptions raised in an event handler will interrupt the request processing.
+- It's simple.
+- The calling order of subscribers is random.
+  You can't set the order in which event handlers are called.
+- Events can't be cancelled.
+  All handlers will always get the event.
+- Event handlers can't have return values.
+- Exceptions raised in an event handler will interrupt the request processing.
 
+For a conceptual overview of events and subscribers, see {doc}`/conceptual-guides/components`.
 
 ## Register an event handler
 
 Plone events can be scoped:
 
--   globally (no scope)
--   per content type
--   per behavior or marker interface
-
+- globally (no scope)
+- per content type
+- per behavior or marker interface
 
 ### Register an event handler on content type creation
 
 The following example demonstrates how to register an event handler when a content type is created.
 
-In your {file}`.product/your/product/configure.zcml` insert the following code.
+In your `.product/your/product/configure.zcml` insert the following code.
 
-{lineno-start=1}
 ```xml
 <subscriber
     for=".interfaces.IMyContentTypeClass
          zope.lifecycleevent.IObjectCreatedEvent"
     handler=".your_python_file.your_method"
-    />
+/>
 ```
 
-The second line defines to which interface you want to bind the execution of your code. 
+The second line defines to which interface you want to bind the execution of your code.
 Here, the event handler code will only be executed if the object is a content type providing the interface `.interfaces.IMyContentTypeClass`.
 If you want this to be interface agnostic, insert an asterix `*` as a wildcard instead.
 
-The third line defines the event on which this should happen, which is `IObjectCreatedEvent`. 
-For more available possible events to use as a trigger, see {ref}`subscribers-event-types-label`. 
+The third line defines the event on which this should happen, which is `IObjectCreatedEvent`.
+For more available possible events to use as a trigger, see {ref}`event-types`.
 
 The fourth line gives the path to the callable function to be executed.
 
-Create your {file}`.product/your/product/your_python_file.py` and insert the following code.
+Create your `.product/your/product/your_python_file.py` and insert the following code.
 
 ```python
 def your_subscriber(object, event):
     # do something with your created content type
 ```
 
-
 ### Subscribe to an event using ZCML
 
-Subscribe to a global event using {term}`ZCML` by inserting the following code in your {file}`.product/your/product/configure.zcml`.
+Subscribe to a global event using ZCML by inserting the following code in your `.product/your/product/configure.zcml`.
 
 ```xml
 <subscriber
     for="Products.PlonePAS.events.UserLoggedOutEvent"
     handler=".smartcard.clear_extra_cookies_on_logout"
-    />
+/>
 ```
 
-For this event, the Python code in {file}`smartcard.py` would be the following.
+For this event, the Python code in `smartcard.py` would be the following.
 
 ```python
 def clear_extra_cookies_on_logout(event):
@@ -99,7 +95,7 @@ The following example for a custom event subscribes content types to all `IMyEve
     for=".interfaces.IMyObject
          .interfaces.IMyEvent"
     handler=".content.MyObject.myEventHandler"
-    />
+/>
 ```
 
 The following example shows how to subscribe a content type to the life cycle event.
@@ -110,10 +106,9 @@ The following example shows how to subscribe a content type to the life cycle ev
     for=".interfaces.ISitsPatient
          zope.lifecycleevent.IObjectModifiedEvent"
     handler=".content.SitsPatient.objectModified"
-    />
+/>
 ```
 
-
 ## Fire an event
 
 Use `zope.event.notify()` to fire event objects to their subscribers.
@@ -128,14 +123,11 @@ event = AfterPublicationEvent(self.portal, self.portal.REQUEST)
 zope.event.notify(event)
 ```
 
-
-(subscribers-event-types-label)=
-
+(event-types)=
 ## Event types
 
 Plone has the following types of events.
 
-
 ### Creation events
 
 `zope.lifecycleevent.IObjectCreatedEvent` is fired for all Zope-ish objects when they are created, or copied via `IObjectCopiedEvent`.
@@ -170,9 +162,3 @@ The DCWorkflow events are low-level events that can tell you a lot about the pre
 `zope.processlifetime.IProcessStarting` is triggered after the component registry has been loaded and Zope is starting up.
 
 `zope.processlifetime.IDatabaseOpened` is triggered after the main ZODB database has been opened.
-
-## Related content
-
--   {doc}`/backend/behaviors`
--   {doc}`/backend/content-types/index`
-