add keyword repeat token filter docs #8149

_analyzers/token-filters/index.md

@@ -35,7 +35,7 @@ Token filter | Underlying Lucene token filter|  Description
 [`keep_types`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keep-types/) | [TypeTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/TypeTokenFilter.html) | Keeps or removes tokens of a specific type.
 [`keep_words`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keep-words/)  | [KeepWordFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeepWordFilter.html) | Checks the tokens against the specified word list and keeps only those that are in the list.
 [`keyword_marker`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keyword-marker/)  | [KeywordMarkerFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordMarkerFilter.html) | Marks specified tokens as keywords, preventing them from being stemmed.
-`keyword_repeat` | [KeywordRepeatFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordRepeatFilter.html) | Emits each incoming token twice: once as a keyword and once as a non-keyword.
+[`keyword_repeat`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/keyword-repeat/) | [KeywordRepeatFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/KeywordRepeatFilter.html) | Emits each incoming token twice: once as a keyword and once as a non-keyword.
 [`kstem`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/kstem/) | [KStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/en/KStemFilter.html) | Provides KStem-based stemming for the English language. Combines algorithmic stemming with a built-in dictionary.
 `kuromoji_completion` | [JapaneseCompletionFilter](https://lucene.apache.org/core/9_10_0/analysis/kuromoji/org/apache/lucene/analysis/ja/JapaneseCompletionFilter.html) | Adds Japanese romanized terms to the token stream (in addition to the original tokens). Usually used to support autocomplete on Japanese search terms. Note that the filter has a `mode` parameter, which should be set to `index` when used in an index analyzer and `query` when used in a search analyzer. Requires the `analysis-kuromoji` plugin. For information about installing the plugin, see [Additional plugins]({{site.url}}{{site.baseurl}}/install-and-configure/plugins/#additional-plugins).
 [`length`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/length/) | [LengthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html) | Removes tokens that are shorter or longer than the length range specified by `min` and `max`. 

_analyzers/token-filters/keyword-repeat.md

@@ -0,0 +1,160 @@
+---
+layout: default
+title: Keyword repeat
+parent: Token filters
+nav_order: 210
+---
+
+# Keyword repeat token filter
+
+The `keyword_repeat` token filter emits the keyword version of a token into a token stream. This filter is typically used when you want to retain both the original token and its modified version after further token transformations, such as stemming or synonym expansion. The duplicated tokens allow the original, unchanged version of the token to remain in the final analysis alongside the modified versions.
+
+The `keyword_repeat` token filter should be placed before stemming filters. Stemming is not applied to every token, thus you may have duplicate tokens in the same position after stemming. To remove duplicate tokens, use the `remove_duplicates` token filter after the stemmer.
+{: .note} 
+
+
+## Example
+
+The following example request creates a new index named `my_index` and configures an analyzer with a `keyword_repeat` filter:
+
+```json
+PUT /my_index
+{
+  "settings": {
+    "analysis": {
+      "filter": {
+        "my_kstem": {
+          "type": "kstem"
+        },
+        "my_lowercase": {
+          "type": "lowercase"
+        }
+      },
+      "analyzer": {
+        "my_custom_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": [
+            "my_lowercase",
+            "keyword_repeat",
+            "my_kstem"
+          ]
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+POST /my_index/_analyze
+{
+  "analyzer": "my_custom_analyzer",
+  "text": "Stopped quickly"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "stopped",
+      "start_offset": 0,
+      "end_offset": 7,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "stop",
+      "start_offset": 0,
+      "end_offset": 7,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "quickly",
+      "start_offset": 8,
+      "end_offset": 15,
+      "type": "<ALPHANUM>",
+      "position": 1
+    },
+    {
+      "token": "quick",
+      "start_offset": 8,
+      "end_offset": 15,
+      "type": "<ALPHANUM>",
+      "position": 1
+    }
+  ]
+}
+```
+
+You can further examine the impact of the `keyword_repeat` token filter by adding the following parameters to the `_analyze` query:
+
+```json
+POST /my_index/_analyze
+{
+  "analyzer": "my_custom_analyzer",
+  "text": "Stopped quickly",
+  "explain": true,
+  "attributes": "keyword"
+}
+```
+{% include copy-curl.html %}
+
+The response includes detailed information, such as tokenization, filtering, and the application of specific token filters:
+
+```json
+{
+  "detail": {
+    "custom_analyzer": true,
+    "charfilters": [],
+    "tokenizer": {
+      "name": "standard",
+      "tokens": [
+        {"token": "OpenSearch","start_offset": 0,"end_offset": 10,"type": "<ALPHANUM>","position": 0},
+        {"token": "helped","start_offset": 11,"end_offset": 17,"type": "<ALPHANUM>","position": 1},
+        {"token": "many","start_offset": 18,"end_offset": 22,"type": "<ALPHANUM>","position": 2},
+        {"token": "employers","start_offset": 23,"end_offset": 32,"type": "<ALPHANUM>","position": 3}
+      ]
+    },
+    "tokenfilters": [
+      {
+        "name": "lowercase",
+        "tokens": [
+          {"token": "opensearch","start_offset": 0,"end_offset": 10,"type": "<ALPHANUM>","position": 0},
+          {"token": "helped","start_offset": 11,"end_offset": 17,"type": "<ALPHANUM>","position": 1},
+          {"token": "many","start_offset": 18,"end_offset": 22,"type": "<ALPHANUM>","position": 2},
+          {"token": "employers","start_offset": 23,"end_offset": 32,"type": "<ALPHANUM>","position": 3}
+        ]
+      },
+      {
+        "name": "keyword_marker_filter",
+        "tokens": [
+          {"token": "opensearch","start_offset": 0,"end_offset": 10,"type": "<ALPHANUM>","position": 0,"keyword": true},
+          {"token": "helped","start_offset": 11,"end_offset": 17,"type": "<ALPHANUM>","position": 1,"keyword": false},
+          {"token": "many","start_offset": 18,"end_offset": 22,"type": "<ALPHANUM>","position": 2,"keyword": false},
+          {"token": "employers","start_offset": 23,"end_offset": 32,"type": "<ALPHANUM>","position": 3,"keyword": false}
+        ]
+      },
+      {
+        "name": "kstem_filter",
+        "tokens": [
+          {"token": "opensearch","start_offset": 0,"end_offset": 10,"type": "<ALPHANUM>","position": 0,"keyword": true},
+          {"token": "help","start_offset": 11,"end_offset": 17,"type": "<ALPHANUM>","position": 1,"keyword": false},
+          {"token": "many","start_offset": 18,"end_offset": 22,"type": "<ALPHANUM>","position": 2,"keyword": false},
+          {"token": "employer","start_offset": 23,"end_offset": 32,"type": "<ALPHANUM>","position": 3,"keyword": false}
+        ]
+      }
+    ]
+  }
+}
+```