The things which are supposed to go into the Model are also allowed to go into the View-Model i.e. Public Properties, IDataErroInfo and INotifyPropertyChanged, then what sho
Business Data + Business Logic + Business Rules
Application UI
Wrapper Over Model which is easily readable/bindable by View using minimum Effort/Code.
IDataErrorInfo - Should go into ViewModelINotifyPropertyChanged - Should go into ViewModel. Could also go in the Model if necessary (But not recommended)