Rework the selector docs to be less abstract

Author: jbaiera

docs/reference/elasticsearch/rest-apis/api-conventions.md

@@ -421,24 +421,24 @@ GET /_nodes/ra*:2
 GET /_nodes/ra*:2*
 ```
 
-### Index Component Selectors [api-component-selectors]
+### Component Selectors [api-component-selectors]
 
-Some APIs that accept a `<data-stream>`, `<index>`, or `<target>` request path parameter also support *selector syntax*.
+A data stream component is a logical grouping of indices that help organize data inside a data stream. All data streams contain a `data` component by default. The `data` component comprises the data stream's backing indices. When searching, managing, or indexing into a data stream, the `data` component is what you are interacting with by default.
 
-Some indices and data streams are made of multiple components besides their default data. These other components store additional data which can be queried separately like regular index data. Some APIs may operate on subsets of these index components which can be specified by using a selector suffix.
+Some data stream features are exposed as additional components alongside its `data` component. These other components are comprised of separate sets of backing indices. These additional components store supplemental data independent of the data stream's regular backing indices. An example of another component is the `failures` component exposed by the data stream [failure store](docs-content://manage-data/data-store/data-streams/failure-store.md) feature, which captures documents that fail to be ingested in a separate set of backing indices on the data stream.
+
+Some APIs that accept a `<data-stream>`, `<index>`, or `<target>` request path parameter also support *selector syntax* which defines which component on a data stream the API should operate on. To use a selector, it is appended to the index or data stream name. Selectors can be combined with other index pattern syntax like [date math](#api-date-math-index-names) and wildcards.
 
 There are currently two selector suffixes supported by {{es}} APIs:
 
 `::data`
-:   (Indices, data streams) This selector references the default component present on all indices and data streams which holds the regular data contained therein.
+:   Refers to a data stream's backing indices containing regular data. Data streams always contain a data component.
 
 `::failures`
-:   (Data streams only) This component references data stored in a data stream's [failure store](docs-content://manage-data/data-store/data-streams/failure-store.md). This component is only present on data streams.
+:   This component refers to the internal indices used for a data stream's [failure store](docs-content://manage-data/data-store/data-streams/failure-store.md).
 
 As an example, [search]({{es-apis}}group/endpoint-search), [field capabilities]({{es-apis}}operation/operation-field-caps), and [index stats]({{es-apis}}operation/operation-indices-stats) APIs can all report results from a different component rather than from the default data.
 
-Selectors are applied to an index pattern at the end and can be combined with other index pattern syntax like [date math](#api-date-math-index-names) and wildcards.
-
 ```console
 # Search for regular data on a data stream
 GET my-data-stream/_search
@@ -454,7 +454,6 @@ GET <logs-{now/d}>::failures/_search
 ```
 
 
-
 ## Parameters [api-conventions-parameters]
 
 Rest parameters (when using HTTP, map to HTTP URL parameters) follow the convention of using underscore casing.