code: void setChainUserIndex(int chain, int index, int value) {
  		int i = getChainIndex_(chain);
  		AttributeStreamOfInt32 stream = m_chainIndices.get(index);
  		if (stream.size() <= i)
  			stream.resize(m_chainData.size(), -1);
  
  		stream.write(i, value);
  	}
docs: Sets a user index value for the chain.