@Override
 public CreaElement addChild(CreaElement element) {
   if (element.getParent() != this) mChildren.add(element.setParent(this));
   return this;
 }
 @Override
 public CreaElement removeChild(CreaElement element) {
   if (element.getParent() == this) mChildren.remove(element.setParent(null));
   return this;
 }