ETag to be matched as a pre-condition for copying the source object
            otherwise returns a PreconditionFailed.
            
 Declaration Syntax
 Declaration Syntax| C# | 
public string ETagToMatch { get; set; }
 Remarks
 Remarks
            Copies the object if its entity tag (ETag) matches 
            the specified tag; otherwise return a 412 (precondition failed).
            Constraints: This property can be used with IfUnmodifiedSince,
            but cannot be used with other conditional copy properties.