:sig
String xml_encode(DValue t)
String xml_encode(DValue t, String root_name)

:params
t : tree to serialize as XML
root_name : optional element name to use when `t` is not already an element-shaped tree, defaults to `root`
return value : XML string

:see
>markup
xml_decode
json_encode
0_DValue
html_escape

:content
Serializes a `DValue` into a simple XML string.

`xml_encode()` does not validate against a schema, DTD, or namespace rules. It is a structural converter for application data, similar in spirit to `json_encode()`.

Try the live example in the [XML demo](../demo/xml.uce).

The native element shape is:

```text
node["name"] = "book"
node["attrs"]["id"] = "b1"
node["text"] = "optional text"
node["children"] = list of child element nodes
```

Example:

```uce
DValue book;
book["name"] = "book";
book["attrs"]["id"] = "b1";

DValue title;
title["name"] = "title";
title["text"] = "UCE & XML";
book["children"].push(title);

String xml = xml_encode(book);
```

The result is:

```xml
<book id="b1"><title>UCE &amp; XML</title></book>
```

For simple map/list/scalar trees, `xml_encode()` creates ordinary child elements:

```uce
DValue payload;
payload["title"] = "Hello";
payload["count"] = "3";

String xml = xml_encode(payload, "payload");
```

Result:

```xml
<payload><count>3</count><title>Hello</title></payload>
```

Notes:

- Element and attribute names are normalized to XML-name-safe strings when needed.
- Text and attribute values are escaped.
- List values use repeated `<item>` children.
- Empty elements serialize as self-closing tags.
- Map child order follows `DValue` map iteration order.
