If i am a user of ContentReaderAttribute.ContentReaderType i am not allowed to write to this Property like ContentReaderAttribute.ContentReaderType = FooBar; so this property is "write protected". I am sorry if my wording is not that precise.

This means also, that from this view perspective, the underlying variable can be read only. 

Thank you for your enligtnment about readonly usage in class in general. Why should that be important for this class/case?