in model/src/main/java/jetbrains/jetpad/model/composite/Composites.java [67:78]
boolean isNonCompositeChild(CompositeT c) {
if (c.getParent() == null) return false;
if (c.nextSibling() != null) return false;
if (c.prevSibling() != null) return false;
List<CompositeT> children = c.getParent().children();
if (children.size() != 1) return true;
if (children.get(0) != c) return true;
return false;
}