Can Server Core and Server with a GUI be mixed in a cluster?

Q. Can I mix Server Core and Server with a GUI Configuration Levels in a cluster?

A. In Windows Server 2012 running cluster validation with a mix of configuration levels would raise an error as the mix was not supported. This changed in Windows Server 2012 R2 and now a validation will result in a warning instead of an error signifying that while supported it is not recommended.