[Backport 2.18] Add keep type docs #8063

_analyzers/token-filters/index.md

@@ -32,7 +32,7 @@ Token filter | Underlying Lucene token filter|  Description
 `flatten_graph` | [FlattenGraphFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/core/FlattenGraphFilter.html) | Flattens a token graph produced by a graph token filter, such as `synonym_graph` or `word_delimiter_graph`, making the graph suitable for indexing.
 `hunspell` | [HunspellStemFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/hunspell/HunspellStemFilter.html) | Uses [Hunspell](https://en.wikipedia.org/wiki/Hunspell) rules to stem tokens. Because Hunspell supports a word having multiple stems, this filter can emit multiple tokens for each consumed token. Requires you to configure one or more language-specific Hunspell dictionaries.
 `hyphenation_decompounder` | [HyphenationCompoundWordTokenFilter](https://lucene.apache.org/core/9_8_0/analysis/common/org/apache/lucene/analysis/compound/HyphenationCompoundWordTokenFilter.html) | Uses XML-based hyphenation patterns to find potential subwords in compound words and checks the subwords against the specified word list. The token output contains only the subwords found in the word list.
-`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_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_word` | [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` | [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.

_analyzers/token-filters/keep-types.md

@@ -0,0 +1,115 @@
+---
+layout: default
+title: Keep types
+parent: Token filters
+nav_order: 180
+---
+
+# Keep types token filter
+
+The `keep_types` token filter is a type of token filter used in text analysis to control which token types are kept or discarded. Different tokenizers produce different token types, for example, `<HOST>`, `<NUM>`, or `<ALPHANUM>`.
+
+The `keyword`, `simple_pattern`, and `simple_pattern_split` tokenizers do not support the `keep_types` token filter because these tokenizers do not support token type attributes.
+{: .note}
+
+## Parameters
+
+The `keep_types` token filter can be configured with the following parameters.
+
+Parameter | Required/Optional | Data type | Description
+:--- | :--- | :--- | :--- 
+`types` | Required | List of strings | List of token types to be kept or discarded (determined by the `mode`).
+`mode`| Optional | String | Whether to `include` or `exclude` the token types specified in `types`. Default is `include`.
+
+
+## Example
+
+The following example request creates a new index named `test_index` and configures an analyzer with a `keep_types` filter:
+
+```json
+PUT /test_index
+{
+  "settings": {
+    "analysis": {
+      "analyzer": {
+        "custom_analyzer": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": ["lowercase", "keep_types_filter"]
+        }
+      },
+      "filter": {
+        "keep_types_filter": {
+          "type": "keep_types",
+          "types": ["<ALPHANUM>"]
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+GET /test_index/_analyze
+{
+  "analyzer": "custom_analyzer",
+  "text": "Hello 2 world! This is an example."
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "hello",
+      "start_offset": 0,
+      "end_offset": 5,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "world",
+      "start_offset": 8,
+      "end_offset": 13,
+      "type": "<ALPHANUM>",
+      "position": 2
+    },
+    {
+      "token": "this",
+      "start_offset": 15,
+      "end_offset": 19,
+      "type": "<ALPHANUM>",
+      "position": 3
+    },
+    {
+      "token": "is",
+      "start_offset": 20,
+      "end_offset": 22,
+      "type": "<ALPHANUM>",
+      "position": 4
+    },
+    {
+      "token": "an",
+      "start_offset": 23,
+      "end_offset": 25,
+      "type": "<ALPHANUM>",
+      "position": 5
+    },
+    {
+      "token": "example",
+      "start_offset": 26,
+      "end_offset": 33,
+      "type": "<ALPHANUM>",
+      "position": 6
+    }
+  ]
+}
+```