add version tag to docs

Author: fang-xing-esql

docs/reference/query-languages/esql/esql-multi-index.md

@@ -136,7 +136,9 @@ FROM events_*
 | 2023-10-23T12:15:03.360Z | 172.21.2.162 | 3450233 | Connected to 10.1.0.3 |
 
 ### Date and date_nanos union type [esql-multi-index-date-date-nanos-union]
-
+```{applies_to}
+stack: ga 9.2.0
+```
 When the type of an {{esql}} field is a *union* of `date` and `date_nanos` across different indices, {{esql}} automatically casts all values to the `date_nanos` type during query execution. This implicit casting ensures that all values are handled with nanosecond precision, regardless of their original type. As a result, users can write queries against such fields without needing to perform explicit type conversions, and the query engine will seamlessly align the types for consistent and precise results.
 
 `date_nanos` fields offer higher precision but have a narrower range of valid values compared to `date` fields. This limits their representable dates roughly from 1970 to 2262. This is because dates are stored as a `long` representing nanoseconds since the epoch. When a field is mapped as both `date` and `date_nanos` across different indices, {{esql}} defaults to the more precise `date_nanos` type. This behavior ensures that no precision is lost when querying multiple indices with differing date field types. For dates that fall outside the valid range of `date_nanos` in fields that are mapped to both `date` and `date_nanos` across different indices, {{esql}} returns null by default. However, users can explicitly cast these fields to the `date` type to obtain a valid value, with precision limited to milliseconds.