Golang结构的XML和JSON标签？

I have an application that can output as JSON or XML depending on the HTTP request headers. I can achieve the correct output for either by adding the correct tags to the structs I'm using, but I can't figure out how to specify the tags for both JSON and XML.

For example, this serializes to correct XML:

type Foo struct {
    Id          int64       `xml:"id,attr"`
    Version     int16       `xml:"version,attr"`
}

...and this generates correct JSON:

type Foo struct {
    Id          int64       `json:"id"`
    Version     int16       `json:"version"`
}

...but this doesn't work for either:

type Foo struct {
    Id          int64       `xml:"id,attr",json:"id"`
    Version     int16       `xml:"version,attr",json:"version"`
}