} else {
                        val underlayElements = underlayItems.map { (it as? ElementNode) ?: error("cannot merge an element $overlayItem with non-elements $underlayItems") }
                        val underlayContent = underlayElements.flatMap(ElementNode::content)

internal
class DefaultDocumentResolutionContainer(
    private val elementResolution: Map<ElementNode, ElementResolution>,
    private val propertyResolution: Map<PropertyNode, PropertyResolution>,
    private val valueFactoryResolution: Map<ValueFactoryNode, ValueFactoryResolution>
) : DocumentResolutionContainer {
    override fun data(node: ElementNode): ElementResolution = elementResolution.getValue(node)

    val valueMapping: MutableMap<DeclarativeDocument.ValueNode, Expr> = mutableMapOf()

    val languageTreeMappingContainer = object : LanguageTreeMappingContainer {
        override fun data(node: DeclarativeDocument.DocumentNode.ElementNode): BlockElement = nodeMapping.getValue(node)
        override fun data(node: DeclarativeDocument.DocumentNode.PropertyNode): BlockElement = nodeMapping.getValue(node)