Add information about Text indexes and dictionary variables (#1026)

Author: JPryce-Aklundh

modules/ROOT/pages/indexes/search-performance-indexes/using-indexes.adoc

@@ -235,14 +235,35 @@ Text indexes do not store `STRING` properties alphabetically, and are instead op
 That said, if no range index had been present on the name property, the previous query would still have been able to utilize the text index.
 It would have done so less efficiently than a range index, but it still would have been useful.
 
-
 For more information about range index ordering, see the section on xref:indexes/search-performance-indexes/using-indexes.adoc#range-index-backed-order-by[Range index-backed ORDER BY].
 
 [TIP]
 Text indexes are only used for exact query matches. To perform approximate matches (including, for example, variations and typos), and to compute a similarity score between `STRING` values, use semantic xref:indexes/semantic-indexes/full-text-indexes.adoc[full-text indexes] instead.
 
 For more information about the predicates supported by text indexes, see xref:indexes/search-performance-indexes/managing-indexes.adoc#text-indexes-supported-predicates[Create, show, and delete indexes -> Text indexes: supported predicates].
 
+[[text-index-dictionary-variables]]
+=== Ensuring text index use
+
+In order for the planner to use text indexes, it must be able to confirm that the properties included in the predicate are `STRING` values.
+This is not possible when accessing property values within nodes or relationships, or values within a `MAP`, since Cypher does not store the type information of these values.
+To ensure text indexes are used in these cases, the xref:functions/string.adoc#functions-tostring[`toString`] function should be used.
+
+.Text index not used
+[source,cypher]
+----
+WITH {name: 'William Shakespeare'} AS varName
+MERGE (:PointOfInterest {name:varName.name})
+----
+
+.Text index used
+[source,cypher]
+----
+WITH {name: 'William Shakespeare'} AS varName
+MERGE (ws:PointOfInterest {name: toString(varName.name)})
+----
+
+For information about how to ensure the use of text indexes when predicates may contain `null` values, see xref:indexes/search-performance-indexes/using-indexes/indexes-and-null[Indexes and `null` values].
 
 [[text-index-string-size]]
 === Text indexes and `STRING` sizes