public void addItems(Collection<? extends Item> items, int at) {
addPlaylist(map(items, Item::toPlaylist), at);
}
public void addPlaylist(Collection<PlaylistItem> ps, int at) {
int _at = at;
<BUG>if (_at < 0)             _at = 0;
if (_at > size()) _at = size();</BUG>
addAll(_at, ps);
updateItems(ps);
}

public void addItems(Collection<? extends Item> items, int at) {
addPlaylist(map(items, Item::toPlaylist), at);
}
public void addPlaylist(Collection<PlaylistItem> ps, int at) {
int _at = at;
if (_at < 0)      _at = 0;
if (_at > size()) _at = size();
addAll(_at, ps);
updateItems(ps);
}
