docs: public String[][] tag2DoubleArray(String src) {
  		if(src==null||src.length()==0)
  			return null;
  		String[] sents = Sentenizer.split(src);
  		String[][] words = new String[sents.length][];
  		for(int i=0;i<sents.length;i++){
  			words[i] = tag2Array(sents[i]);
  		}		
  		return words;
  	}