docs: public static String genSequence6Tags(String[] wordArray){
  		StringBuilder sb = new StringBuilder();
  		for(int i=0; i<wordArray.length; i++) {
  			String word = wordArray[i];
  			String tag = null;
  			int len = word.length();
  			switch(len){
  			case 1:
  				tag = "S";break;
  			case 2:
  				tag = "BE";break;
  			case 3:
  				tag = "B2E";break;
  			case 4:
  				tag = "B23E";break;
  			default :
  				tag = "B23";
  				int rest = len-4;
  				while(rest-->0){
  					tag+="M";
  				}
  				tag+="E";
  			}
  			assert tag.length() ==len;
  			for(int j=0; j<word.length(); j++) {
  				char c = word.charAt(j);	
  				sb.append(c);
  				sb.append('\t');
  				sb.append(tag.charAt(j));
  				sb.append('\n');
  			}
  		}
  		sb.append('\n');
  		return sb.toString();
  	}