[DOCS] Add collapsible sections to 8.0 breaking changes [Part 3] (#56297

)

docs/reference/migration/migrate_8_0/http.asciidoc

@@ -8,16 +8,31 @@
 
 // end::notable-breaking-changes[]
 
-[float]
-==== Removal of old HTTP settings
-
+.The `http.tcp_no_delay` setting has been replaced by `http.tcp.no_delay`.
+[%collapsible]
+====
+*Details* +
 The `http.tcp_no_delay` setting was deprecated in 7.x and has been removed in 8.0. It has been replaced by
 `http.tcp.no_delay`.
 
-[float]
-==== Changes to Encoding Plus Signs in URLs
+*Impact* +
+Use the `http.tcp.no_delay` setting. Discontinue use of the `http.tcp_no_delay`
+setting. Specifying the `http.tcp_no_delay` setting in `elasticsearch.yml` will
+result in an error on startup.
+====
 
+.The `es.rest.url_plus_as_space` system property has been removed.
+[%collapsible]
+====
+*Details* +
 Starting in version 7.4, a `+` in a URL will be encoded as `%2B` by all REST API functionality. Prior versions handled a `+` as a single space.
-If your application requires handling `+` as a single space you can return to the old behaviour by setting the system property
+In these previous versions, if your application required handling `+` as a single space, you could return to the old behaviour by setting the system property
 `es.rest.url_plus_as_space` to `true`. Note that this behaviour is deprecated and setting this system property to `true` will cease
-to be supported in version 8.
+to be supported in version 8.
+
+*Impact* +
+Update your workflow and applications to assume `+` in a URL is encoded as
+`%2B`. Discontinue use of the `es.rest.url_plus_as_space` system property.
+Specifying this property in `elasticsearch.yml` will result in an error on
+startup.
+====

docs/reference/migration/migrate_8_0/ilm.asciidoc

@@ -9,16 +9,35 @@
 
 // end::notable-breaking-changes[]
 
-[float]
 [[ilm-poll-interval-limit]]
-==== `indices.lifecycle.poll_interval` must be greater than 1 second
-
+.The `indices.lifecycle.poll_interval` setting must be greater than `1s`.
+[%collapsible]
+====
+*Details* +
 The setting `indices.lifecycle.poll_interval`, if set too low, can cause
-excessive load on a cluster. This setting must now be set to 1 second or higher.
+excessive load on a cluster. This setting must now be set to `1s` (one second)
+or greater.
 
-[float]
-[[ilm-hlrc-rename]]
-==== `indexlifecycle` packages renamed to `ilm`
+*Impact* +
+Update the `indices.lifecycle.poll_interval` setting to a value of `1s` or
+greater using `elasticsearch.yml` or the
+{ref}/cluster-update-settings.html[cluster update settings API].
 
+Setting `indices.lifecycle.poll_interval` to less than `1s` in
+`elasticsearch.yml` will result in an error on startup.
+{ref}/cluster-update-settings.html[Cluster update settings API] requests that
+set `indices.lifecycle.poll_interval` to less than `1s` will return an error.
+====
+
+[[ilm-hlrc-rename]]
+.The `indexlifecycle` package has been renamed `ilm` in the Java High Level REST Client.
+[%collapsible]
+====
+*Details* +
 In the high level REST client, the `indexlifecycle` package has been
-renamed to `ilm` to match the package rename inside the Elasticsearch code.
+renamed to `ilm` to match the package rename inside the {es} code.
+
+*Impact* +
+Update your workflow and applications to use the `ilm` package in place of
+`indexlifecycle`.
+====

docs/reference/migration/migrate_8_0/indices.asciidoc

@@ -8,52 +8,86 @@
 //tag::notable-breaking-changes[]
 //end::notable-breaking-changes[]
 
-[float]
-==== Force Merge API changes
 
-Previously, the Force Merge API allowed the parameters `only_expunge_deletes`
+.The force merge API's `max_num_segments` and `only_expunge_deletes` parameters cannot both be specified in the same request.
+[%collapsible]
+====
+*Details* +
+Previously, the force merge API allowed the parameters `only_expunge_deletes`
 and `max_num_segments` to be set to a non default value at the same time. But
 the `max_num_segments` was silently ignored when `only_expunge_deletes` is set
 to `true`, leaving the false impression that it has been applied.
 
-The Force Merge API now rejects requests that have a `max_num_segments` greater
-than or equal to 0 when the `only_expunge_deletes` is set to true.
-
-[float]
-==== On-disk term dictionary cannot be disabled
+*Impact* +
+When using the {ref}/indices-forcemerge.html[force merge API], do not specify
+values for both the `max_num_segments` and `only_expunge_deletes` parameters.
+Requests that include values for both parameters will return an error.
+====
 
+.The `index.force_memory_term_dictionary` setting has been removed.
+[%collapsible]
+====
+*Details* +
 The `index.force_memory_term_dictionary` setting was introduced in 7.0 as a
 temporary measure to allow users to opt-out of the optimization that leaves the
 term dictionary on disk when appropriate. This optimization is now mandatory
 and the setting is removed.
 
-[float]
-==== Remove support for `template` in put index template requests
-
-In 6.0, we deprecated the `template` field in put index template requests
-in favor of using `index_patterns`. Support for the `template` field is now
+*Impact* +
+Discontinue use of the `index.force_memory_term_dictionary` index setting.
+Requests that include this setting will return an error.
+====
+
+.The put index template API's `template` parameter has been removed.
+[%collapsible]
+====
+*Details* +
+In 6.0, we deprecated the `template` parameter in put index template requests
+in favor of using `index_patterns`. Support for the `template` parameter is now
 removed in 8.0.
 
+*Impact* +
+Use the {ref}/indices-templates-v1.html[put index template API]'s
+`index_patterns` parameter. Requests that include the `template` parameter will
+return an error.
+====
 
-[float]
-==== Remove synced flush
-
+.Synced flush has been removed.
+[%collapsible]
+====
+*Details* +
 Synced flush was deprecated in 7.6 and is removed in 8.0. Use a regular flush
 instead as it has the same effect as a synced flush in 7.6 and later.
 
+*Impact* +
+Use the {ref}/indices-flush.html[flush API]. Requests to the
+`/<index>/flush/synced` or `/flush/synced` endpoints will return an error.
+====
 
-[float]
-==== Indices with soft deletes disabled
-
+.The `index.soft_deletes.enabled` setting has been removed.
+[%collapsible]
+====
+*Details* +
 Creating indices with soft deletes disabled was deprecated in 7.6 and
-is no longer supported in 8.0. The setting index.soft_deletes.enabled
-can no longer be set to false. As the setting defaults to true, simply
-leave the setting unset.
-
-[float]
-==== Translog retention settings are no longer supported
-
-Translog retention settings `index.translog.retention.size` and
-`index.translog.retention.age` were effectively ignored in 7.4,
-deprecated in 7.7, and removed in 8.0 in favor of
-<<index-modules-history-retention,soft deletes>>.
+is no longer supported in 8.0. The `index.soft_deletes.enabled` setting
+can no longer be set to `false`. 
+
+*Impact* +
+Discontinue use of the `index.soft_deletes.enabled` index setting. Requests that
+set `index.soft_deletes.enabled` to `false` will return an error.
+====
+
+.The `index.translog.retention.age` and `index.translog.retention.size` settings have been removed.
+[%collapsible]
+====
+*Details* +
+Translog retention settings `index.translog.retention.age` and
+`index.translog.retention.size` were effectively ignored in 7.4, deprecated in
+7.7, and removed in 8.0 in favor of
+{ref}/index-modules-history-retention.html[soft deletes].
+
+*Impact* +
+Discontinue use of the `index.translog.retention.age` and
+`index.translog.retention.size` index settings. Requests that
+include these settings will return an error.
+====