Add further considerations for CASE expressions (#1013)

Co-authored-by: Jens Pryce-Åklundh <[email protected]>

Author: gem-neo4j

modules/ROOT/pages/queries/case.adoc

@@ -323,3 +323,29 @@ RETURN n.name, n.colorCode
 |===
 
 For more information about using the `SET` clause, see xref::clauses/set.adoc[SET].
+
+== Further considerations
+
+`CASE` result branches are statically checked prior to execution. 
+This means that if a branch is not semantically correct, it will still throw an exception, even if that branch may never be executed during runtime.
+
+In the following example, `date` is statically known to be a `STRING` value, and therefore would fail if treated as a `DATE` value. 
+
+.Not allowed
+[source, cypher, role=test-fail]
+----
+WITH "2024-08-05" AS date, "string" AS type
+RETURN CASE type
+    WHEN "string" THEN datetime(date)
+    WHEN "date" THEN datetime({year: date.year, month: date.month, day: date.day})
+    ELSE datetime(date)
+END AS dateTime
+----
+
+.Error message
+[source, error]
+----
+Type mismatch: expected Map, Node, Relationship, Point, Duration, Date, Time, LocalTime, LocalDateTime or DateTime but was String (line 4, column 38 (offset: 136))
+"    WHEN 'date' THEN datetime({year: date.year, month: date.month, day: date.day})"
+                                      ^
+----