docs: add field paths/wildcards cross-reference to expressions reference

Link to the mapping doc for dot notation, escaping, wildcards, and
contextualization datasets. These field path features apply to both
data flows and data flow graphs.

Author: jlian

articles/iot-operations/connect-to-cloud/concept-dataflow-graphs-expressions.md

@@ -266,6 +266,16 @@ JSON objects and arrays are preserved as-is when fields are copied without an ex
 
 ¹ Available in data flow graphs only. Not supported in data flow `builtInTransformation` inputs.
 
+## Field paths, wildcards, and contextualization
+
+The expression language operates on fields referenced in the `inputs` and `output` of each rule. For details on how to reference fields, including dot notation, escaping, wildcard matching, and contextualization datasets, see [Map data by using data flows](concept-dataflow-mapping.md). These field path features apply to both data flows and data flow graphs.
+
+Key features:
+
+- **Dot notation**: Reference nested fields like `Employee.DateOfBirth` or escape segments containing dots like `"Tag.10"`.
+- **Wildcards**: Use `*` in input and output paths to match multiple fields at once, for example `ColorProperties.*`.
+- **Contextualization datasets**: Reference external data with `$context(datasetName).fieldName`.
+
 ## Related content
 
 - [Map data by using data flows](concept-dataflow-mapping.md)