<target-index> | String | The index to get settings from. Can be a comma-separated list to get settings from multiple indexes, or use `_all` to return settings from all indexes within the cluster.
<setting> | String | Filter to return specific settings.
allow_no_indices | Boolean | Whether to ignore wildcards that don’t match any indexes. Default is `true`.
expand_wildcards | String | Expands wildcard expressions to different indexes. Combine multiple values with commas. Available values are `all` (match all indexes), `open` (match open indexes), `closed` (match closed indexes), `hidden` (match hidden indexes), and `none` (do not accept wildcard expressions), which must be used with `open`, `closed`, or both. Default is `open`.
flat_settings | Boolean | Whether to return settings in the flat form, which can improve readability, especially for heavily nested settings. For example, the flat form of “index”: { “creation_date”: “123456789” } is “index.creation_date”: “123456789”.