Add new default date format

_field-types/supported-field-types/date.md

@@ -58,7 +58,11 @@ Parameter | Description
 
 ## Formats
 
-OpenSearch has built-in date formats, but you can also create your own custom formats. The default format is `strict_date_time_no_millis||strict_date_optional_time||epoch_millis`. You can specify multiple date formats, separated by `||`.
+OpenSearch has built-in date formats, but you can also create your own custom formats. You can specify multiple date formats, separated by `||`.
+
+## Default format
+
+As of OpenSearch 2.12, the default date format is `strict_date_time_no_millis||strict_date_optional_time||epoch_millis`. To revert the default format back to `strict_date_optional_time||epoch_millis` (the default format for OpenSearch 2.11 and earlier), set the `opensearch.experimental.optimization.datetime_formatter_caching.enabled` feature flag to `false`. For more information about enabling and disabling feature flags, see [Enabling experimental features]({{site.url}}{{site.baseurl}}/experimental/).
 
 ## Built-in formats
 
@@ -223,7 +227,7 @@ GET testindex/_search
 
 The date field type supports using date math to specify durations in queries. For example, the `gt`, `gte`, `lt`, and `lte` parameters in [range queries]({{site.url}}{{site.baseurl}}/query-dsl/term/range/) and the `from` and `to` parameters in [date range aggregations]({{site.url}}{{site.baseurl}}/query-dsl/aggregations/bucket/date-range/) accept date math expressions.
 
-A date math expression contains a fixed date, optionally followed by one or more mathematical expressions. The fixed date may be either `now` (current date and time in milliseconds since the epoch) or a string ending with `||` that specifies a date (for example, `2022-05-18||`). The date must be in the `strict_date_time_no_millis||strict_date_optional_time||epoch_millis` format.
+A date math expression contains a fixed date, optionally followed by one or more mathematical expressions. The fixed date may be either `now` (current date and time in milliseconds since the epoch) or a string ending with `||` that specifies a date (for example, `2022-05-18||`). The date must be in the [default format](#default-format), which by default is `strict_date_time_no_millis||strict_date_optional_time||epoch_millis`.
 
 If you specify multiple date formats in the field mapping, OpenSearch uses the first format to convert the milliseconds since the epoch value to a string. <br>
 If a field mapping for a field contains no format, OpenSearch uses `strict_date_optional_time` to convert the epoch value to a string.

_search-plugins/concurrent-segment-search.md

@@ -31,7 +31,7 @@ There are several methods for enabling concurrent segment search, depending on t
 If you are running an OpenSearch cluster and want to enable concurrent segment search in the config file, add the following line to `opensearch.yml`:
 
 ```yaml
-opensearch.experimental.feature.concurrent_segment_search.enabled=true
+opensearch.experimental.feature.concurrent_segment_search.enabled: true
 ```
 {% include copy.html %}
 

experimental.md

@@ -0,0 +1,89 @@
+---
+layout: default
+title: Enabling experimental features
+nav_order: 10
+parent: OpenSearch documentation
+---
+
+# Enabling experimental features
+
+OpenSearch releases may contain experimental features that you can enable or disable as needed. There are several methods for enabling feature flags, depending on the installation type. 
+
+## Enable in opensearch.yml
+
+If you are running an OpenSearch cluster and want to enable feature flags in the config file, add the following line to `opensearch.yml`:
+
+```yaml
+opensearch.experimental.feature.<feature_name>.enabled: true
+```
+{% include copy.html %}
+
+## Enable on Docker containers
+
+If you’re running Docker, add the following line to `docker-compose.yml` under the `opensearch-node` > `environment` section:
+
+```bash
+OPENSEARCH_JAVA_OPTS="-Dopensearch.experimental.feature.<feature_name>.enabled=true"
+```
+{% include copy.html %}
+
+## Enable on a tarball installation
+
+To enable feature flags on a tarball installation, provide the new JVM parameter either in `config/jvm.options` or `OPENSEARCH_JAVA_OPTS`.
+
+### Option 1: Modify jvm.options
+
+Add the following lines to `config/jvm.options` before starting the `opensearch` process to enable the feature and its dependency:
+
+```bash
+-Dopensearch.experimental.feature.<feature_name>.enabled=true
+```
+{% include copy.html %}
+
+Then run OpenSearch:
+
+```bash
+./bin/opensearch
+```
+{% include copy.html %}
+
+### Option 2: Enable with an environment variable
+
+As an alternative to directly modifying `config/jvm.options`, you can define the properties by using an environment variable. This can be done using a single command when you start OpenSearch or by defining the variable with `export`.
+
+To add the feature flags inline when starting OpenSearch, run the following command:
+
+```bash
+OPENSEARCH_JAVA_OPTS="-Dopensearch.experimental.feature.<feature_name>.enabled=true" ./opensearch-{{site.opensearch_version}}/bin/opensearch
+```
+{% include copy.html %}
+
+If you want to define the environment variable separately prior to running OpenSearch, run the following commands:
+
+```bash
+export OPENSEARCH_JAVA_OPTS="-Dopensearch.experimental.feature.<feature_name>.enabled=true"
+```
+{% include copy.html %}
+
+```bash
+./bin/opensearch
+```
+{% include copy.html %}
+
+## Enable for OpenSearch development
+
+To enable feature flags for development, you must add the correct properties to `run.gradle` before building OpenSearch. See the [Developer Guide](https://github.com/opensearch-project/OpenSearch/blob/main/DEVELOPER_GUIDE.md) for information about to use how Gradle to build OpenSearch.
+
+Add the following properties to run.gradle to enable the feature:
+
+```gradle
+testClusters {
+    runTask {
+      testDistribution = 'archive'
+      if (numZones > 1) numberOfZones = numZones
+      if (numNodes > 1) numberOfNodes = numNodes
+      systemProperty 'opensearch.experimental.feature.<feature_name>.enabled', 'true'
+    }
+  }
+```
+{% include copy.html %}