[DOCS] Add 7.9 breaking change for built-in templates (#61549) (#61558)

docs/reference/data-streams/set-up-a-data-stream.asciidoc

@@ -111,14 +111,18 @@ template for a data stream must specify:
 [IMPORTANT]
 ====
 {es} has built-in index templates for the `metrics-*-*` and `logs-*-*` index
-patterns. {ingest-guide}/ingest-management-overview.html[{agent}] uses these
-templates to create data streams. If you use {agent}, assign your index
-templates a priority lower than `100` to avoid an override of the built-in
-templates.
+patterns, each with a priority of `100`.
+{ingest-guide}/ingest-management-overview.html[{agent}] uses these templates to
+create data streams. If you use {agent}, assign your index templates a priority
+lower than `100` to avoid overriding the built-in templates.
 
 Otherwise, to avoid accidentally applying the built-in templates, use a
-non-overlapping index pattern, or assign your templates a `priority` higher or
-lower than `100`.
+non-overlapping index pattern or assign templates with an overlapping pattern a
+`priority` higher than `100`.
+
+For example, if you don't use {agent} and want to create a template for the
+`logs-*` index pattern, assign your template a priority of `200`. This ensures
+your template is applied instead of the built-in template for `logs-*-*`.
 ====
 
 Every document indexed to a data stream must have a `@timestamp` field. This

docs/reference/docs/index_.asciidoc

@@ -172,14 +172,18 @@ the operation automatically creates the index and applies any matching
 [IMPORTANT]
 ====
 {es} has built-in index templates for the `metrics-*-*` and `logs-*-*` index
-patterns. {ingest-guide}/ingest-management-overview.html[{agent}] uses these
-templates to create data streams. If you use {agent}, assign your index
-templates a priority lower than `100` to avoid an override of the built-in
-templates.
+patterns, each with a priority of `100`.
+{ingest-guide}/ingest-management-overview.html[{agent}] uses these templates to
+create data streams. If you use {agent}, assign your index templates a priority
+lower than `100` to avoid overriding the built-in templates.
 
 Otherwise, to avoid accidentally applying the built-in templates, use a
-non-overlapping index pattern, or assign your templates a `priority` higher or
-lower than `100`.
+non-overlapping index pattern or assign templates with an overlapping pattern a
+`priority` higher than `100`.
+
+For example, if you don't use {agent} and want to create a template for the
+`logs-*` index pattern, assign your template a priority of `200`. This ensures
+your template is applied instead of the built-in template for `logs-*-*`.
 ====
 
 If no mapping exists, the index operation

docs/reference/indices/index-templates.asciidoc

@@ -23,14 +23,18 @@ If a new data stream or index matches more than one index template, the index te
 [IMPORTANT]
 ====
 {es} has built-in index templates for the `metrics-*-*` and `logs-*-*` index
-patterns. {ingest-guide}/ingest-management-overview.html[{agent}] uses these
-templates to create data streams. If you use {agent}, assign your index
-templates a priority lower than `100` to avoid an override of the built-in
-templates.
+patterns, each with a priority of `100`.
+{ingest-guide}/ingest-management-overview.html[{agent}] uses these templates to
+create data streams. If you use {agent}, assign your index templates a priority
+lower than `100` to avoid an overriding the built-in templates.
 
 Otherwise, to avoid accidentally applying the built-in templates, use a
-non-overlapping index pattern, or assign your templates a `priority` higher or
-lower than `100`.
+non-overlapping index pattern or assign templates with an overlapping pattern a
+`priority` higher than `100`.
+
+For example, if you don't use {agent} and want to create a template for the
+`logs-*` index pattern, assign your template a priority of `200`. This ensures
+your template is applied instead of the built-in template for `logs-*-*`.
 ====
 
 When a composable template matches a given index

docs/reference/indices/put-index-template.asciidoc

@@ -87,14 +87,18 @@ used to match the names of data streams and indices during creation.
 [IMPORTANT]
 ====
 {es} has built-in index templates for the `metrics-*-*` and `logs-*-*` index
-patterns. {ingest-guide}/ingest-management-overview.html[{agent}] uses these
-templates to create data streams. If you use {agent}, assign your index
-templates a priority lower than `100` to avoid an override of the built-in
-templates.
+patterns, each with a priority of `100`.
+{ingest-guide}/ingest-management-overview.html[{agent}] uses these templates to
+create data streams. If you use {agent}, assign your index templates a priority
+lower than `100` to avoid an overriding the built-in templates.
 
 Otherwise, to avoid accidentally applying the built-in templates, use a
-non-overlapping index pattern, or assign your templates a `priority` higher or
-lower than `100`.
+non-overlapping index pattern or assign templates with an overlapping pattern a
+`priority` higher than `100`.
+
+For example, if you don't use {agent} and want to create a template for the
+`logs-*` index pattern, assign your template a priority of `200`. This ensures
+your template is applied instead of the built-in template for `logs-*-*`.
 ====
 
 [xpack]#`data_stream`#::

docs/reference/migration/migrate_7_9.asciidoc

@@ -9,12 +9,41 @@ your application to {es} 7.9.
 
 See also <<release-highlights>> and <<es-release-notes>>.
 
+* <<breaking_79_indices_changes>>
 * <<breaking_79_script_cache_changes>>
 * <<breaking_79_settings_changes>>
 
 //NOTE: The notable-breaking-changes tagged regions are re-used in the
 //Installation and Upgrade Guide
 
+//tag::notable-breaking-changes[]
+[discrete]
+[[breaking_79_indices_changes]]
+=== Indices changes
+.{es} includes built-in index templates for `logs-*-*` and `metrics-*-*`.
+
+[%collapsible]
+====
+*Details* +
+In 7.9, {es} added built-in index templates for the `metrics-*-*` and
+`logs-*-*` index patterns, each with a priority of `100`.
+{ingest-guide}/ingest-management-overview.html[{agent}] uses these templates to
+create data streams.
+
+*Impact* +
+If you use {agent}, assign your index templates a priority
+lower than `100` to avoid overriding the built-in templates.
+
+Otherwise, to avoid accidentally applying the built-in templates, use a
+non-overlapping index pattern or assign templates with an overlapping pattern a
+`priority` higher than `100`.
+
+For example, if you don't use {agent} and want to use a template for the
+`logs-*` index pattern, assign your template a priority of `200`. This ensures
+your template is applied instead of the built-in template for `logs-*-*`.
+====
+//end::notable-breaking-changes[]
+
 //tag::notable-breaking-changes[]
 [discrete]
 [[breaking_79_script_cache_changes]]