I'm marshalling this type:

585 type Resource struct {
586     XMLName      xml.Name `xml:"res"`
587     ProtocolInfo string   `xml:"protocolInfo,attr"`
588     URL          string   `xml:",chardata"`
589     Size         uint64   `xml:"size,attr"`
590     Bitrate      uint     `xml:"bitrate,attr"`
591     Duration     *string   `xml:"duration,attr"`
592 }

Which returns an error on the Duration field:

xml: unsupported type: *string

I'm using the tip.

Marshal purports to support this:

"Marshal handles a pointer by marshalling the value it points at or, if the pointer
is nil, by writing nothing."