Add escape note for map keys

Author: baanders

articles/digital-twins/how-to-query-graph.md

@@ -5,7 +5,7 @@ titleSuffix: Azure Digital Twins
 description: See how to query the Azure Digital Twins twin graph for information.
 author: baanders
 ms.author: baanders # Microsoft employees only
-ms.date: 02/23/2022
+ms.date: 03/02/2023
 ms.topic: how-to
 ms.service: digital-twins
 ms.custom: contperf-fy21q2
@@ -59,6 +59,8 @@ You can also get twins based on the type of a property. Here's a query that gets
 >[!TIP]
 > If a property is of type `Map`, you can use the map keys and values directly in the query, like this:
 > :::code language="sql" source="~/digital-twins-docs-samples/queries/examples.sql" id="QueryByProperty4":::
+>
+> If the map key starts with a numeric character, you'll need to wrap the key in double square brackets (`[[<mapKey>]]`) to escape it in the query, similar to the strategy for [querying with reserved keywords](reference-query-reserved.md#escaping-reserved-keywords-in-queries).
 
 ## Query by model