Documentation about the hints annotation for processors

CHANGELOG.next.asciidoc

@@ -115,6 +115,7 @@ https://github.com/elastic/beats/compare/v7.0.0-alpha2...main[Check the HEAD dif
 
 *Filebeat*
 
+- Extend documentation about hints annotation for processors {pull}30561[30561]
 
 *Heartbeat*
 

filebeat/docs/autodiscover-hints.asciidoc

@@ -79,6 +79,41 @@ co.elastic.logs/raw: "[{\"containers\":{\"ids\":[\"${data.container.id}\"]},\"mu
 Define a processor to be added to the {beatname_uc} input/module configuration. See <<filtering-and-enhancing-data>> for the list
 of supported processors.
 
+If processors configuration uses list data structure, object fields must be enumerated.
+For example, hints for the `rename` processor configuration below
+[source,yaml]
+-----
+processors:
+  - rename:
+      fields:
+        - from: "a.g"
+          to: "e.d"
+      fail_on_error: true
+-----
+will look like:
+[source,yaml]
+-----
+co.elastic.logs/processors.rename.fields.0.from: "a.g"
+co.elastic.logs/processors.rename.fields.1.to: "e.d"
+co.elastic.logs/processors.rename.fail_on_error: 'true'
+-----
+
+If processors configuration uses map data structure, enumeration is not needed. For example, the equivalent to the `add_fields` configuration below
+[source,yaml]
+-----
+processors:
+  - add_fields:
+      target: project
+      fields:
+        name: myproject
+-----
+is
+[source,yaml]
+-----
+co.elastic.logs/processors.1.add_fields.target: "project"
+co.elastic.logs/processors.1.add_fields.fields.name: "myproject"
+-----
+
 In order to provide ordering of the processor definition, numbers can be provided. If not, the hints builder will do
 arbitrary ordering: