Fix call-by-value section

specification.md

@@ -220,10 +220,33 @@ Even further, one cannot assign to a variable of array type.
 
 #### Call by Value / Call by Reference
 
-`bool`, `int`, and `float` are passed directly (by value).
+`bool`, `int`, and `float` are passed by value.
-Strings and arrays are passed via pointers internally (by reference).
+For arrays and strings a pointer is passed by value (similar to C).
 
-Modifications made to an array inside a function are visible outside of that function.
+Modifications made to an array inside a function are visible outside the function.
+
+    void foo(int[5] arr) {
+        arr[2] = 42;
+    }
+
+    void main() {
+        int[5] arr;
+        foo(arr);
+        print_int(arr[2]); // outputs 42
+    }
+
+While strings can be re-assigned (in contrast to arrays), this is not visible outside the function call.
+
+    void foo(string s) {
+        s = "foo";
+    }
+
+    void main() {
+        string s;
+        s = "bar";
+        foo(s);
+        print(s); // outputs bar
+    }
 
 #### Type Conversion