Golang encoding/xml: invalid unsupported type error

Go version

go version go1.24.0 windows/amd64

Output of go env in your module/workspace:

!

What did you do?

using this code:

package main

import "encoding/xml"

func main() {
   var value struct {
      Envelope struct {
         Soap string `xml:"soap,attr"`
      }
   }
   _, err := xml.Marshal(value.Envelope)
   if err != nil {
      panic(err)
   }
}

I get this result:

xml: unsupported type: struct { Soap string "xml:\"soap,attr\"" }

this result appears to be invalid:

the name of the struct field used to obtain the data

https://go.dev/pkg/encoding/xml?m=old#Marshal

from the documentation, xml.Marshal should take the name for XML element from the name of the struct field, in this case "Envelope"

What did you see happen?

!

What did you expect to see?

!