Copies the object if it has not been modified since the specified time, otherwise returns a PreconditionFailed.
            
 Declaration Syntax
 Declaration Syntax| C# | 
public DateTime UnmodifiedSinceDate { get; set; }
 Remarks
 Remarks
            Copies the object if it hasn't been modified since the
            specified time; otherwise returns a 412 (precondition failed).
            Constraints: This property can be used with ETagToMatch,
            but cannot be used with other conditional copy properties.