Document how to disable diazo for ajax requests and completly.

docs/classic-ui/theming/diazo.md

@@ -176,3 +176,68 @@ For instance, you may need to put together the main menu, the language change, a
 Sometimes it is easier to override the corresponding template in Plone, build the new HTML structure there, and replace one thing in the {file}`rules.xml` file than trying to write complex Diazo rules or writing XSLT.
 
 The size of the {file}`rules.xml` file and the number of rules it contains can negatively impact the performance of your site.
+
+
+### Disable Diazo for AJAX requests
+
+After sending an AJAX request from the client to Plone, Plone returns a JSON response.
+Normally, this response should not get transformed by Diazo themes, and is usually handled in client-side JavaScript.
+
+To prevent this transformation, disable AJAX requests for Diazo themes by using the `ajax_load` HTTP request parameter.
+`ajax_load` is used in Plone to indicate AJAX requests.
+When added to the query string, `ajax_load=1` disables a full page rendering, whereas `ajax_load=0` enables it.
+
+````{versionadded} Plone 6.2
+In Plone 6.2, the query parameter and its value `ajax_load=1` are automatically added to most AJAX requests by default.
+
+```{seealso}
+See the related pull request [Automatically set the ajax_load request parameter, `plone/Products.CMFPlone` #4169](https://github.com/plone/Products.CMFPlone/pull/4169).
+```
+````
+
+Manually add the HTTP request parameter and its value as follows.
+
+Add a theme parameter to your {file}`manifest.cfg` file.
+
+```cfg
+[theme:parameters]
+ajax_load = python:request.get('ajax_load')
+```
+
+Then disable Diazo for AJAX requests in your {file}`rules.xml` file.
+
+```xml
+<notheme if="$ajax_load" /><!-- don't theme ajax requests -->
+```
+
+Choose any method to load this change in your theme.
+
+-   Restart your instance.
+-   In the {guilabel}`Theming` control panel, select another theme, then switch back to your own theme.
+-   For a programmatical way, see [(Re)Introduce the ajax_load theme parameter and skip diazo theming, if set. `plone/plonetheme.barceloneta` #404](https://github.com/plone/plonetheme.barceloneta/pull/404).
+
+
+### Completely disable Diazo
+
+You can fully disable Diazo for your theme.
+
+Set the `X-Theme-Disabled` HTTP header before Diazo gets active, such as in an `IBeforeTraverseEvent` event subscriber, as shown in the following example.
+
+Add an event subscriber in a {file}`subscribers.py` file in an add-on package.
+
+```python
+def disable_diazo(obj, event):
+    event.request.response.setHeader("X-Theme-Disabled", True)
+```
+
+Then register it in a {file}`configure.zcml` file.
+
+```xml
+<subscriber
+  for="*
+       zope.traversing.interfaces.IBeforeTraverseEvent"
+  handler=".subscribers.disable_diazo"
+/>
+```
+
+Now Diazo should be disabled for all requests.