encoding/xml handle unmapped elements

From http://golang.org/pkg/encoding/xml/#Unmarshal

> * If the XML element contains a sub-element that hasn't matched any of the above rules and the struct has a field with tag ",any",
> unmarshal maps the sub-element to that struct field.

I'm having trouble getting the remainder of an XML envelope into my struct (to show that I have an incomplete mapping)

http://play.golang.org/p/mnFqAcguJQ

I know you can use exactly this method with bson.M from the mgo packages using ,inline - but it looks like map[string]interface{} isn't the answer here.

EDIT:
After some additional playing, I've found what I believe to be some additional unexpected behavior.

Switching to []string as a type starts to accept input, but no key/value pairs: http://play.golang.org/p/wCAJeeQa4m

I also planned on adapting encode/xml in order to parse html. I do not see in the documentation that if an element exists more than once, it will save the last instance of it, rather than erroring out: http://play.golang.org/p/0MY__R-Xi3

Here: http://play.golang.org/p/iY8YlxYym0

Since c is something concrete, it shouldn't use ",any", hence it should have a struct definition. C itself contains a list of arbitrary tags, hence it should contain an []Tag xml:'",any"'... now to capture the Tag itself, you need xml.Name to get the tag name and something with ",innerxml".

Finally the result is this:

const xmlString = `<foo><a>1</a><b>2</b><c><c1>3</c1><c2>4</c2></c></foo>`
type Foo struct {
	A int   `xml:"a"`
	B int   `xml:"b"`
	C Extra `xml:"c"`
}

type Extra struct {
	Items []Tag `xml:",any"`
}

type Tag struct {
	XMLName xml.Name
	Content string `xml:",innerxml"`
}

Or the shorter version:

type Foo struct {
	A int   `xml:"a"`
	B int   `xml:"b"`
	C struct {
		Items []struct {
			XMLName xml.Name
			Content string `xml:",innerxml"`
		} `xml:",any"`
	} `xml:"c"`
}

For HTML there is go.net/html. Using xml parser for html will be complicated.