Add lowercase token filter docs (#8162)

* add lowercase token filter Signed-off-by: Anton Rubin <[email protected]> * adding examples in greek to lowercase token filter #8154 Signed-off-by: Anton Rubin <[email protected]> * Update lowercase.md Signed-off-by: AntonEliatra <[email protected]> * Doc review Signed-off-by: Fanit Kolchina <[email protected]> * Apply suggestions from code review Co-authored-by: Nathan Bower <[email protected]> Signed-off-by: kolchfa-aws <[email protected]> --------- Signed-off-by: Anton Rubin <[email protected]> Signed-off-by: AntonEliatra <[email protected]> Signed-off-by: Fanit Kolchina <[email protected]> Signed-off-by: kolchfa-aws <[email protected]> Co-authored-by: Fanit Kolchina <[email protected]> Co-authored-by: kolchfa-aws <[email protected]> Co-authored-by: Nathan Bower <[email protected]>
opensearch-project · Dec 2, 2024 · c0d158f · c0d158f
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diff --git a/_analyzers/token-filters/index.md b/_analyzers/token-filters/index.md
@@ -40,7 +40,7 @@ Token filter | Underlying Lucene token filter|  Description
 `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`. 
 `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)).
+[`lowercase`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/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) processes the English language. To process other languages, 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`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/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.
 [`multiplexer`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/multiplexer/) | N/A | Emits multiple tokens at the same position. Runs each token through each of the specified filter lists separately and outputs the results as separate tokens.
 [`ngram`]({{site.url}}{{site.baseurl}}/analyzers/token-filters/ngram/) | [NGramTokenFilter](https://lucene.apache.org/core/9_10_0/analysis/common/org/apache/lucene/analysis/ngram/NGramTokenFilter.html) | Tokenizes the given token into n-grams of lengths between `min_gram` and `max_gram`.

diff --git a/_analyzers/token-filters/lowercase.md b/_analyzers/token-filters/lowercase.md
@@ -0,0 +1,82 @@
+---
+layout: default
+title: Lowercase
+parent: Token filters
+nav_order: 260
+---
+
+# Lowercase token filter
+
+The `lowercase` token filter is used to convert all characters in the token stream to lowercase, making searches case insensitive.
+
+## Parameters
+
+The `lowercase` token filter can be configured with the following parameter.
+
+Parameter | Required/Optional | Description
+:--- | :--- | :---
+ `language` | Optional | Specifies a language-specific token filter. Valid values are: <br>- [`greek`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/el/GreekLowerCaseFilter.html) <br>-  [`irish`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/ga/IrishLowerCaseFilter.html) <br>-  [`turkish`](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/tr/TurkishLowerCaseFilter.html). <br> Default is the [Lucene LowerCaseFilter](https://lucene.apache.org/core/8_7_0/analyzers-common/org/apache/lucene/analysis/core/LowerCaseFilter.html). 
+
+## Example
+
+The following example request creates a new index named `custom_lowercase_example`. It configures an analyzer with a `lowercase` filter and specifies `greek` as the `language`:
+
+```json
+PUT /custom_lowercase_example
+{
+  "settings": {
+    "analysis": {
+      "analyzer": {
+        "greek_lowercase_example": {
+          "type": "custom",
+          "tokenizer": "standard",
+          "filter": ["greek_lowercase"]
+        }
+      },
+      "filter": {
+        "greek_lowercase": {
+          "type": "lowercase",
+          "language": "greek"
+        }
+      }
+    }
+  }
+}
+```
+{% include copy-curl.html %}
+
+## Generated tokens
+
+Use the following request to examine the tokens generated using the analyzer:
+
+```json
+GET /custom_lowercase_example/_analyze
+{
+  "analyzer": "greek_lowercase_example",
+  "text": "Αθήνα ΕΛΛΑΔΑ"
+}
+```
+{% include copy-curl.html %}
+
+The response contains the generated tokens:
+
+```json
+{
+  "tokens": [
+    {
+      "token": "αθηνα",
+      "start_offset": 0,
+      "end_offset": 5,
+      "type": "<ALPHANUM>",
+      "position": 0
+    },
+    {
+      "token": "ελλαδα",
+      "start_offset": 6,
+      "end_offset": 12,
+      "type": "<ALPHANUM>",
+      "position": 1
+    }
+  ]
+}
+```