Improve WITH shadowing examples to clarify behavior (#591)

I have slightly changed the wording as a result of #542, and also
expanded the first two relevant examples so that the error you would get
is shown (as was already the case in the section `COLLECT subquery with
WITH`).

Author: stefano-ottolenghi

modules/ROOT/pages/syntax/expressions.adoc

@@ -518,7 +518,7 @@ RETURN person.name AS name, EXISTS {
 [[existential-subquery-with-union]]
 ==== `EXISTS` subquery with a `UNION`
 
-_This feature was introduced in Neo4j 5.3._ 
+_This feature was introduced in Neo4j 5.3._
 
 `Exists` can be used with a `UNION` clause, and the `RETURN` clauses are not required.
 It is worth noting that if one branch has a `RETURN` clause, then all branches require one.
@@ -551,12 +551,34 @@ RETURN
 [[existential-subquery-with-with]]
 ==== `EXISTS` subquery with `WITH`
 
-_This feature was introduced in Neo4j 5.3._ 
+_This feature was introduced in Neo4j 5.3._
 
 Variables from the outside scope are visible for the entire subquery, even when using a `WITH` clause.
-This means that shadowing of these variables is not allowed.
+To avoid confusion, shadowing of these variables is not allowed.
 An outside scope variable is shadowed when a newly introduced variable within the inner scope is defined with the same variable.
-In the below example, a `WITH` clause introduces a new variable.
+In the example below, the outer variable `name` is shadowed and will therefore throw an error.
+
+.Query
+[source, cypher, role=test-fail]
+----
+WITH 'Peter' as name
+MATCH (person:Person {name: name})
+WHERE EXISTS {
+    WITH "Ozzy" AS name
+    MATCH (person)-[:HAS_DOG]->(d:Dog)
+    WHERE d.name = name
+}
+RETURN person.name AS name
+----
+
+.Error message
+[source, output, role="noheader"]
+----
+The variable `name` is shadowing a variable with the same name from the outer scope and needs to be renamed (line 4, column 20 (offset: 90))
+----
+
+New variables can be introduced into the subquery, as long as they use a different identifier.
+In the example below, a `WITH` clause introduces a new variable.
 Note that the outer scope variable `person` referenced in the main query is still available after the `WITH` clause.
 
 .Query
@@ -583,7 +605,7 @@ RETURN person.name AS name
 [[existential-subquery-with-return]]
 ==== `EXISTS` subquery with `RETURN`
 
-_This feature was introduced in Neo4j 5.3._ 
+_This feature was introduced in Neo4j 5.3._
 
 `EXISTS` subqueries do not require a `RETURN` clause at the end of the subquery. If one is present, it does not
 need to be aliased, which is different compared to xref::clauses/call-subquery.adoc[`CALL` subqueries].
@@ -713,9 +735,31 @@ RETURN
 _This feature was introduced in Neo4j 5.3._
 
 Variables from the outside scope are visible for the entire subquery, even when using a `WITH` clause.
-This means that shadowing of these variables is not allowed.
+To avoid confusion, shadowing of these variables is not allowed.
 An outside scope variable is shadowed when a newly introduced variable within the inner scope is defined with the same variable.
-In the below example, a `WITH` clause introduces a new variable.
+In the example below, the outer variable `name` is shadowed and will therefore throw an error.
+
+.Query
+[source, cypher, role=test-fail]
+----
+WITH 'Peter' as name
+MATCH (person:Person {name: name})
+WHERE COUNT {
+    WITH "Ozzy" AS name
+    MATCH (person)-[:HAS_DOG]->(d:Dog)
+    WHERE d.name = name
+} = 1
+RETURN person.name AS name
+----
+
+.Error message
+[source, output, role="noheader"]
+----
+The variable `name` is shadowing a variable with the same name from the outer scope and needs to be renamed (line 4, column 20 (offset: 90))
+----
+
+New variables can be introduced into the subquery, as long as they use a different identifier.
+In the example below, a `WITH` clause introduces a new variable.
 Note that the outer scope variable `person` referenced in the main query is still available after the `WITH` clause.
 
 .Query
@@ -974,9 +1018,9 @@ RETURN
 ==== `COLLECT` subquery with `WITH`
 
 Variables from the outside scope are visible for the entire subquery, even when using a `WITH` clause.
-This means that shadowing of these variables is not allowed.
+To avoid confusion, shadowing of these variables is not allowed.
 An outside scope variable is shadowed when a newly introduced variable within the inner scope is defined with the same variable.
-In the below example, the outer variable `name` is shadowed and will therefore throw an error.
+In the example below, the outer variable `name` is shadowed and will therefore throw an error.
 
 .Query
 [source, cypher, role=test-fail]
@@ -997,7 +1041,7 @@ The variable `name` is shadowing a variable with the same name from the outer sc
 ----
 
 New variables can be introduced into the subquery, as long as they use a different identifier.
-In the below example, a `WITH` clause introduces a new variable.
+In the example below, a `WITH` clause introduces a new variable.
 Note that the outer scope variable `person` referenced in the main query is still available after the `WITH` clause.
 
 .Query