duplicateNode method
Duplicate node
and add it to the children list.
Implementation
DOMNode? duplicateNode(DOMNode node) {
if (isEmptyContent) return null;
var idx = indexOfNodeIdenticalFirst(node);
if (idx < 0) return null;
var elem = _content![idx];
var copy = elem.copy();
_content!.insert(idx + 1, copy);
copy.parent = this;
return copy;
}