adding normalizer mapping parameter docs

_field-types/mapping-parameters/normalizer.md

@@ -0,0 +1,92 @@
+---
+layout: default
+title: Normalizer
+parent: Mapping parameters
+grand_parent: Mapping and field types
+nav_order: 110
+has_children: false
+has_toc: false
+---
+
+# Normalizer
+
+The `normalizer` mapping parameter defines a custom normalization process for keyword fields. Unlike [analyzers]({{site.url}}{{site.baseurl}}/analyzers/supported-analyzers/index/) for text fields, which generate multiple tokens, [normalizers]({{site.url}}{{site.baseurl}}/analyzers/normalizers/) transform the entire field value into a single token using a set of token filters. When you define a normalizer, the keyword field is processed by the specified filters before it is stored while keeping the `_source` of the document unchanged.
+
+
+## Defining a normalizer
+
+The following request creates an index named `products` with a custom normalizer called `my_normalizer`. The normalizer is applied to the `code` field, which uses the `trim` and `lowercase` filters:
+
+```json
+PUT /products
+{
+  "settings": {
+    "analysis": {
+      "normalizer": {
+        "my_normalizer": {
+          "type": "custom",
+          "filter": ["trim", "lowercase"]
+        }
+      }
+    }
+  },
+  "mappings": {
+    "properties": {
+      "code": {
+        "type": "keyword",
+        "normalizer": "my_normalizer"
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+When you ingest a document into the index, the `code` field is normalized by trimming any extra spaces and converting the text to lowercase:
+
+```json
+PUT /products/_doc/1
+{
+  "code": "  ABC-123 EXTRA  "
+}
+```
+{% include copy-curl.html %}
+
+Search for the indexed document using lowercase and trimmed text in the query:
+
+```json
+POST /products/_search
+{
+  "query": {
+    "term": {
+      "code": "abc-123 extra"
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+Because the `code` field is normalized, the `term` query successfully matches the stored document:
+
+```json
+{
+...
+  "hits": {
+    "total": {
+      "value": 1,
+      "relation": "eq"
+    },
+    "max_score": 0.2876821,
+    "hits": [
+      {
+        "_index": "products",
+        "_id": "1",
+        "_score": 0.2876821,
+        "_source": {
+          "code": "  ABC-123 EXTRA  "
+        }
+      }
+    ]
+  }
+}
+```