Document the @@render-portlet view.

README.rst

@@ -5,6 +5,34 @@ plone.app.portlets provides a Plone-specific user interface for
 plone.portlets, as well as a standard set of portlets that ship with Plone.
 
 
+Call one portlet by URL
+=======================
+
+To call a portlet by its URL, for example, to update it via an AJAX call, use
+the `@@render-portlet` view in your portlet renderer with `portlethash` as a
+query parameter.
+
+The following example shows how to construct a reload URL for a portlet::
+
+    from plone.app.portlets.portlets.base import Renderer
+    from Products.CMFPlone.utils import safe_unicode
+
+
+    class BasePortletRenderer(Renderer):
+        @property
+        def hash(self):
+            portlethash = self.request.form.get(
+                "portlethash", getattr(self, "__portlet_metadata__", {}).get("hash", "")
+            )
+            return portlethash
+
+        @property
+        def reload_url(self):
+            base_url = self.context.absolute_url()
+            hash = safe_unicode(self.hash)
+            return f"{base_url}/@@render-portlet?portlethash={hash}"
+
+
 Compatibility
 =============
 

news/+document-portlet-renderer.documentation.rst

@@ -0,0 +1,4 @@
+Document the @@render-portlet view.
+Documentation about the @@render-portlet view, which can be used to reload a
+portlet via AJAX.
+@thet