Hi,
I am trying to work out how to visually group states on a state-chart without using a composite state. While attempting to use a `rectangle` for this purpose I found that just enabling `allow_mixing` raises errors for any existing composite state declarations. Furthermore the input and output nodes seem to now be illegal. Please see the below which shows both these issues.
```
@startuml
allow_mixing
title MixingErrorExample
rectangle "node" {
state One
state Two
}
' error with below line
[*] -> One
One -> Two:as
' error with below line
state Three {
}
@enduml
```
