Add length token filter docs #8152

Signed-off-by: Anton Rubin <[email protected]>

_analyzers/token-filters/index.md

@@ -36,7 +36,7 @@ Token filter | Underlying Lucene token filter|  Description
 `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` | [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` | [LengthFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LengthFilter.html) | Removes tokens whose lengths are shorter or longer than the length range specified by `min` and `max`. 
+[`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 whose lengths are shorter or longer than the length range specified by `min` and `max`. 
 `limit` | [LimitTokenCountFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/miscellaneous/LimitTokenCountFilter.html) | Limits the number of output tokens. A common use case is to limit the size of document field values based on token count.
 `lowercase` | [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) | Converts tokens to lowercase. The default [LowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/LowerCaseFilter.html) is for the English language. You can set the `language` parameter to `greek` (uses [GreekLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/el/GreekLowerCaseFilter.html)), `irish` (uses [IrishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.html)), or `turkish` (uses [TurkishLowerCaseFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/tr/TurkishLowerCaseFilter.html)).
 `min_hash` | [MinHashFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/minhash/MinHashFilter.html) | Uses the [MinHash technique](https://en.wikipedia.org/wiki/MinHash) to estimate document similarity. Performs the following operations on a token stream sequentially: <br> 1. Hashes each token in the stream. <br> 2. Assigns the hashes to buckets, keeping only the smallest hashes of each bucket. <br> 3. Outputs the smallest hash from each bucket as a token stream.

_analyzers/token-filters/length.md

@@ -0,0 +1,89 @@
+---
+layout: default
+title: Length
+parent: Token filters
+nav_order: 240
+---
+
+# Length token filter
+
+The `length` token filter in OpenSearch is used to remove tokens from the token stream that don't meet specified length criteria, such as min and max values.
+
+## Parameters
+
+The `length` token filter in OpenSearch can be configured with the following parameters:
+
+- `min`: Minimum length of tokens that should be created. Default is `0` (Integer, _Optional_)
+- `max`: Maximum length of tokens that should be created. Default is `2147483647` (Integer, _Optional_)
+
+
+## Example
+
+The following example request creates a new index named `my_index` and configures an analyzer with `length` filter:
+
+```json
+PUT my_index
+{
+  "settings": {
+    "analysis": {
+      "analyzer": {
+        "only_keep_4_to_10_characters": {
+          "tokenizer": "whitespace",
+          "filter": [ "length_4_to_10" ]
+        }
+      },
+      "filter": {
+        "length_4_to_10": {
+          "type": "length",
+          "min": 4,
+          "max": 10
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the created analyzer:
+
+```json
+GET /my_index/_analyze
+{
+  "analyzer": "only_keep_4_to_10_characters",
+  "text": "OpenSearch is a great tool!"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "OpenSearch",
+      "start_offset": 0,
+      "end_offset": 10,
+      "type": "word",
+      "position": 0
+    },
+    {
+      "token": "great",
+      "start_offset": 16,
+      "end_offset": 21,
+      "type": "word",
+      "position": 3
+    },
+    {
+      "token": "tool!",
+      "start_offset": 22,
+      "end_offset": 27,
+      "type": "word",
+      "position": 4
+    }
+  ]
+}
+```