docs: public static String genCrossLabel(String sent,String delim,String delimTag,Set<String> filter){
  		sent = sent.trim();
  		if(sent.length()==0)
  			return sent;
  		StringBuilder sb = new StringBuilder();
  		String[] wordArray = sent.split(delim);
  		for(int i=0; i<wordArray.length; i++) {
  			//得到tag
  			int idx = wordArray[i].lastIndexOf(delimTag);
  			if(idx==-1||idx==wordArray[i].length()-1){
  				System.err.println(wordArray[i]);
  			}			
  			String word = wordArray[i].substring(0,idx);
  			String tag = wordArray[i].substring(idx+1);
  			for(int j=0; j<word.length(); j++) {
  				char c = word.charAt(j);	
  				sb.append(c);
  				sb.append('\t');
  				if(filter==null||filter.contains(tag)){//不过滤或是保留项					
  					if(j == 0) {
  						if(word.length() == 1)
  							sb.append("S-"+tag);
  						else
  							sb.append("B-"+tag);
  					} else if(j == word.length()-1) {
  						sb.append("E-"+tag);
  					} else {
  						sb.append("M-"+tag);
  					}
  				}else{//过滤项
  					sb.append("O");
  				}
  				sb.append('\n');
  			}
  		}
  		sb.append('\n');
  		return sb.toString();
  	}