code: int createPathUserIndex() {
  		if (m_pathindices == null)
  			m_pathindices = new ArrayList<AttributeStreamOfInt32>(0);
  		// Try getting existing index. Use linear search. We do not expect many
  		// indices to be created.
  		for (int i = 0; i < m_pathindices.size(); i++) {
  			if (m_pathindices.get(i) == null) {
  				m_pathindices.set(i,
  						(AttributeStreamOfInt32) (AttributeStreamBase
  								.createIndexStream(0)));
  				return i;
  			}
  		}
  
  		m_pathindices.add((AttributeStreamOfInt32) (AttributeStreamBase
  				.createIndexStream(0)));
  		return (int) (m_pathindices.size() - 1);
  	}
docs: index allows to store an integer user value on the path.