JAXB unmarshalling ? Sax reader ? What about… nothing.

Here is a very tiny and naive xml parser made in kotlin.
One function, one input (string), one output (map).
Simple, and lightweight (no library).

private fun xmlToMap(body: String): Map, Any> {
    val OPENING_TAG = Regex("^< ([^ >/]+)[^>]*>")
    val OPENING_CLOSING_TAG = Regex("^< ([^ >/]+)[^>]*/>")
    val CLOSING_TAG = Regex("^]+)>")
    val ATTRS = Regex("([a-zA-Z][a-zA-Z-0-9]*)=\"([^\"]*)\"")
    val root = mutableMapOf, Any>()

    val deque = ArrayDeque(listOf(root))

    val attrSetFunc = {text: String, node: MutableMap, Any> ->
        ATTRS.findAll(text).forEach { node[it.groups[1]!!.value] = it.groups[2]!!.value } }

    var substring = body
    var currentNode = root
    while(substring.isNotEmpty()){
        when{
            OPENING_CLOSING_TAG.containsMatchIn(substring) -> {
                val groups = OPENING_CLOSING_TAG.find(substring)!!.groups
                val localName = groups[1]!!.value
                val attrs = mutableMapOf, Any>()
                attrSetFunc(groups[0]!!.value, attrs)
                currentNode[localName] = attrs
                substring = substring.substring(groups[0]!!.range.endInclusive+1)
            }
            CLOSING_TAG.containsMatchIn(substring) -> {
                val groups = CLOSING_TAG.find(substring)!!.groups
                currentNode = deque.pop()
                substring = substring.substring(groups[0]!!.range.endInclusive+1)
            }
            OPENING_TAG.containsMatchIn(substring) -> {
                val groups = OPENING_TAG.find(substring)!!.groups
                attrSetFunc(groups[0]!!.value, currentNode)
                val localName = groups[1]!!.value
                deque.push(currentNode)
                currentNode[localName] = mutableMapOf, Any>()
                currentNode = currentNode[localName] as MutableMap, Any>
                substring = substring.substring(groups[0]!!.range.endInclusive+1)

            }
            else -> {
                val data = substring.substring(0 until substring.indexOf('< '))
                currentNode["CDATA"] = data
                substring = substring.substring(substring.indexOf('< '))
            }
        }
    }
    return root
}