Nitpicks and some other enhancement comments resolved

Author: mridula-s109

docs/reference/elasticsearch/rest-apis/retrievers/linear-retriever.md

@@ -38,6 +38,10 @@ Combining `query` and `retrievers` is not supported.
     When used with the [multi-field query format](../retrievers.md#multi-field-query-format) (`query` parameter), normalizes scores per [field grouping](../retrievers.md#multi-field-field-grouping).
     Otherwise serves as the default normalizer for any sub-retriever that doesn't specify its own normalizer. Per-retriever normalizers always take precedence over the top-level normalizer.
 
+    :::{note}
+    **Top-level normalizer support for sub-retrievers**: The ability to use a top-level normalizer as a default for sub-retrievers was introduced in Elasticsearch 9.2+. In earlier versions, only per-retriever normalizers are supported.
+    :::
+
     ::::{warning}
     Avoid using `none` as that will disable normalization and may bias the result set towards lexical matches.
     See [field grouping](../retrievers.md#multi-field-field-grouping) for more information.
@@ -80,6 +84,7 @@ Each entry in the `retrievers` array specifies the following parameters:
     Specifies how the retriever's score will be normalized before applying the specified `weight`.
     See [normalizers](#linear-retriever-normalizers) for supported values.
     If not specified, uses the top-level `normalizer` or defaults to `none` if no top-level normalizer is set.
+    {applies_to}`stack: ga 9.2`
 
 See also [this hybrid search example](retrievers-examples.md#retrievers-examples-linear-retriever) using a linear retriever on how to independently configure and apply normalizers to retrievers.
 

x-pack/plugin/rank-rrf/src/test/java/org/elasticsearch/xpack/rank/linear/LinearRetrieverBuilderParsingTests.java

@@ -75,7 +75,7 @@ protected LinearRetrieverBuilder createTestInstance() {
                 new CompoundRetrieverBuilder.RetrieverSource(TestRetrieverBuilder.createRandomTestRetrieverBuilder(), null)
             );
             weights[i] = randomFloat();
-            normalizers[i] = randomFrom(SCORE_NORMALIZERS);
+            normalizers[i] = randomScoreNormalizer();
         }
 
         return new LinearRetrieverBuilder(innerRetrievers, fields, query, normalizer, rankWindowSize, weights, normalizers);

x-pack/plugin/rank-rrf/src/yamlRestTest/resources/rest-api-spec/test/linear/10_linear_retriever.yml

@@ -1514,66 +1514,6 @@ setup:
   - match: { hits.total.value: 0 }
   - length: { hits.hits: 0 }
 
----
-"Linear retriever with per-retriever normalizer override":
-  - requires:
-      cluster_features: [ "linear_retriever.top_level_normalizer" ]
-      reason: "Support for top-level normalizer in linear retriever"
-  - do:
-      search:
-        index: test
-        body:
-          retriever:
-            linear:
-              normalizer: minmax
-              retrievers: [
-                {
-                  retriever: {
-                    standard: {
-                      query: {
-                        constant_score: {
-                          filter: {
-                            term: {
-                              keyword: {
-                                value: "one"
-                              }
-                            }
-                          },
-                          boost: 5.0
-                        }
-                      }
-                    }
-                  },
-                  weight: 1.0,
-                  normalizer: l2_norm
-                },
-                {
-                  retriever: {
-                    standard: {
-                      query: {
-                        constant_score: {
-                          filter: {
-                            term: {
-                              keyword: {
-                                value: "four"
-                              }
-                            }
-                          },
-                          boost: 12.0
-                        }
-                      }
-                    }
-                  },
-                  weight: 1.0
-                }
-              ]
-
-  - match: { hits.total.value: 2 }
-  - match: { hits.hits.0._id: "1" }
-  - match: { hits.hits.1._id: "4" }
-  - close_to: { hits.hits.0._score: { value: 1.0, error: 0.001} }
-  - close_to: { hits.hits.1._score: { value: 1.0, error: 0.001} }
-
 ---
 "Linear retriever with mixed normalizers - inheritance test":
   - requires:
@@ -1657,6 +1597,10 @@ setup:
   # Third retriever: L2 norm on [6.0] = 1.0, final = 1.0 * 2.0 = 2.0
   - match: { hits.hits.0._id: "3" }  # Highest score due to weight=2.0
   - close_to: { hits.hits.0._score: { value: 2.0, error: 0.001} }
+  - match: { hits.hits.1._id: "1" }  # Second score = 1.0
+  - close_to: { hits.hits.1._score: { value: 1.0, error: 0.001} }
+  - match: { hits.hits.2._id: "2" }  # Third score = 1.0
+  - close_to: { hits.hits.2._score: { value: 1.0, error: 0.001} }
 
 ---
 "Linear retriever with identity normalizer (no normalization)":