How do I convert an ISO8601 TimeSpan to a C# TimeSpan?

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I am getting a \[code\]System.FormatException\[/code\] when I try to do the following (as an example):\[code\]TimeSpan ts = XmlConvert.ToTimeSpan("P72H");\[/code\]I've investigated the ISO8601 Standard and it seems to be correct, but I cannot get it to parse hours without throwing an exception, no matter what I do.Thanks!EDIT: Exception detail:\[code\]System.FormatException was unhandled by user codeHResult=-2146233033Message=The string 'P72H' is not a valid TimeSpan value.Source=System.Xml\[/code\]