diff --git a/foomo/docs/projects/gotsrpc/playground/02_wheel-of-fortune.md b/foomo/docs/projects/gotsrpc/playground/02_wheel-of-fortune.md
index 89f4242..3197e78 100644
--- a/foomo/docs/projects/gotsrpc/playground/02_wheel-of-fortune.md
+++ b/foomo/docs/projects/gotsrpc/playground/02_wheel-of-fortune.md
@@ -4,6 +4,8 @@ Spin the Wheel of Fortune to win a price.
 
 [http://localhost:8080/wheel-of-fortune](http://localhost:8080/wheel-of-fortune)
 
+This example shows the union feature as described here: [../service-interfaces/value-objects#union-types](../service-interfaces/value-objects#union-types)
+
 ## Go service
 
 Service interface defintion
diff --git a/foomo/docs/projects/gotsrpc/playground/03_todos.md b/foomo/docs/projects/gotsrpc/playground/03_todos.md
index 3161ae1..4f43197 100644
--- a/foomo/docs/projects/gotsrpc/playground/03_todos.md
+++ b/foomo/docs/projects/gotsrpc/playground/03_todos.md
@@ -1,5 +1,6 @@
 # Todos
 
+There was a time, when building a todo app was the default demo, so here is one for you.:
 ## Go Service
 
 Service interface defintion
diff --git a/foomo/docs/projects/gotsrpc/playground/04_union-errors.md b/foomo/docs/projects/gotsrpc/playground/04_union-errors.md
index f943e8d..e4c9d19 100644
--- a/foomo/docs/projects/gotsrpc/playground/04_union-errors.md
+++ b/foomo/docs/projects/gotsrpc/playground/04_union-errors.md
@@ -4,19 +4,19 @@
 
 Service interface defintion
 
-```go reference title="server/services/wof/service.go" lines
+```go reference title="server/services/ouch/service.go" lines
 https://github.com/foomo/gotsrpc-playground/blob/main/server/services/ouch/service.go
 ```
 
 Service implementation
 
-```go reference title="server/services/helloworld/service.go"
+```go reference title="server/services/ouch/service.go"
 https://github.com/foomo/gotsrpc-playground/blob/main/server/server/ouch.go
 ```
 
 
 ## Next.js TypeScript client
 
-```typescript reference title="client/pages/wheel-of-fortune.tsx"
+```typescript reference title="client/pages/ouch.tsx"
 https://github.com/foomo/gotsrpc-playground/blob/main/client/pages/ouch.tsx
 ```
diff --git a/foomo/docs/projects/gotsrpc/playground/05_playground.md b/foomo/docs/projects/gotsrpc/playground/05_playground.md
new file mode 100644
index 0000000..f8221b3
--- /dev/null
+++ b/foomo/docs/projects/gotsrpc/playground/05_playground.md
@@ -0,0 +1,24 @@
+# Playground
+
+The playground is not for documentation - it is there to play with the service interface, the server implementation and the generated gotsrpc code.
+
+## Go Service
+
+Service interface defintion
+
+```go reference title="server/services/playground/service.go" lines
+https://github.com/foomo/gotsrpc-playground/blob/main/server/services/playground/service.go
+```
+
+Service implementation
+
+```go reference title="server/services/playground/service.go"
+https://github.com/foomo/gotsrpc-playground/blob/main/server/server/playground.go
+```
+
+
+## Next.js TypeScript client
+
+```typescript reference title="client/pages/playground.tsx"
+https://github.com/foomo/gotsrpc-playground/blob/main/client/pages/playground.tsx
+```
diff --git a/foomo/docs/projects/gotsrpc/service-interfaces/value-objects.md b/foomo/docs/projects/gotsrpc/service-interfaces/value-objects.md
index df6447c..da5ef46 100644
--- a/foomo/docs/projects/gotsrpc/service-interfaces/value-objects.md
+++ b/foomo/docs/projects/gotsrpc/service-interfaces/value-objects.md
@@ -273,3 +273,6 @@ type Basic interface {
 }
 ```
 
+### Union Types
+
+When static types seem to be in the way