EnvDTE CodeModel: CodeType vs CodeTypeRef

[John Esquel]

Hello,

I have the following question about MS Code Model classes
[it's probably simple but I have not much experience in it]:

What is the exact difference between the classes in EnvDTE namespace:
CodeType vs CodeTypeRef ?
What do they represent, could you give me any example ?

From MSDN I understand nothing i.e. the is only small note for the classes:
CodeType: "Represents a class construct in a source file"
CodeTypeRef : "An object defining the type of a construct in a source
file"

I don't understand it :-(

Thanks in advance,

John Esquel