docs: public void copy(VertexData data) {
          clear();
          indices.addAll(data.indices);
          final TIntObjectIterator<VertexAttribute> iterator = data.attributes.iterator();
          while (iterator.hasNext()) {
              iterator.advance();
              attributes.put(iterator.key(), iterator.value().clone());
          }
          nameToIndex.putAll(data.nameToIndex);
      }