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/Program.cs

using System;
using System.Linq;
using System.Xml.Linq;
using System.Xml.XPath;
					
public class Program
{
	public static void Main()
	{
		var xml = @"
		         <ShipmentHeader>
            <DocumentID>62017836-1</DocumentID>
            <DocumentReference type=""CustomerSuppliedReference"">
               <DocumentID>
                  <ID>10532</ID>
               </DocumentID>
            </DocumentReference>
            <Status>
               <Code/>
               <Description languageID=""en-us""/>
            </Status>
            <ActualShipDateTime>2023-06-07T09:16:33-04:00</ActualShipDateTime>
            <ShippingMethod>CHEAPEST METHOD W/FIRST CLASS</ShippingMethod>
            <DocumentReference type=""TrackingNumber"">
               <TrackingNumber>9200190233107605458375</TrackingNumber>
            </DocumentReference>
         </ShipmentHeader>
";
		var doc = XDocument.Parse(xml);

		var result1 = 
			doc.Root
			   .Elements("DocumentReference")
			   .Where(e => (string)e.Attribute("type") == "TrackingNumber")
			   .SelectMany(e => e.Elements("TrackingNumber"))
			   .Select(e => e.Value);

		result1.Dump();

		var result2 = doc.XPathSelectElements(
		  @"/ShipmentHeader/DocumentReference[@type=""TrackingNumber""]/TrackingNumber")
			.Select(e => e.Value);

		result2.Dump();
	}
}