Message in Spanish (Español)
El elemento raíz '<var>X</var>' debe implementar IProvideCustomContentState, o bien un controlador de eventos Navigating debe establecer la propiedad NavigatingCancelEventArgs.ContentStateToSave.
Unlocalized message
'<var>X</var>' root element must implement IProvideCustomContentState, or a Navigating event handler must set NavigatingCancelEventArgs.ContentStateToSave property.
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