syntax - Go String after variable declaration

Take a look at this snip found at here

import (
    "encoding/xml"
    "fmt"
    "os"
)

func main() {
    type Address struct {

        City, State string
    }
    type Person struct {
        XMLName   xml.Name `xml:"person"`
        Id        int      `xml:"id,attr"`
        FirstName string   `xml:"name>first"`
        LastName  string   `xml:"name>last"`
        Age       int      `xml:"age"`
        Height    float32  `xml:"height,omitempty"`
        Married   bool

        Address
        Comment string `xml:",comment"`
    }

    v := &Person{Id: 13, FirstName: "John", LastName: "Doe", Age: 42}
    v.Comment = " Need more details. "
    v.Address = Address{"Hanga Roa", "Easter Island"}

    enc := xml.NewEncoder(os.Stdout)
    enc.Indent("  ", "    ")

    if err := enc.Encode(v); err != nil {
        fmt.Printf("error: %v\n", err)
    }

}

I can understand in the struct Person, It has a var called Id, which is of type int, but what about the stuff

xml:"person" 

after int? What does it mean? Thanks.

Answer

It's a struct tag. Libraries use these to annotate struct fields with extra information; in this case, the module encoding/xml uses these struct tags to denote which tags correspond to the struct fields.