You're seeing just the function
field_schema_nested, go back to ExAliyunOts.Search module for more information.
field_schema_nested( "content", field_schemas: [ field_schema_keyword("header"), field_schema_keyword("body"), ]
:field_schemas, required, the nested field schema(s);
:index, specifies whether to set as index, by default it is true;
:store, specifies whether to store the origin value in search index for a better read performance, by default it is true;
:enable_sort_and_agg, specifies whether to support sort and statistics, by default it is true.