Represents an XML element with tag and attributes; a namespaced name is written {uri; local}
XMLElement[tag, {attr1 -> val1, …}, {data1, …}]
ExportString[XMLElement["tag", {"attr" -> "value"}, {"data"}], "XML"]
→ <tag attr='value'>data</tag>ExportString[XMLElement["tag", {"attr" -> "value"}, {"data", XMLElement["tag2", {}, {"data2"}]}], "XML"]
→ <tag attr='value'>data<tag2>data2</tag2></tag>