tree data UPDATE error for wrong xpath return type
diff --git a/src/tree_data.h b/src/tree_data.h
index 7d1e51d..1414bcc 100644
--- a/src/tree_data.h
+++ b/src/tree_data.h
@@ -2453,7 +2453,7 @@
* (unless they are defined in top-level). Other predicates can still follow the aforementioned ones.
*
* @param[in] ctx_node XPath context node.
- * @param[in] xpath [XPath](@ref howtoXPath) to select in JSON format.
+ * @param[in] xpath [XPath](@ref howtoXPath) to select in JSON format. It must evaluate into a node set.
* @param[out] set Set of found data nodes. In case the result is a number, a string, or a boolean,
* the returned set is empty.
* @return LY_SUCCESS on success, @p set is returned.