code: public boolean appendPrefix(int tl, int td, StringBuffer sb) {
      if (dr.scopeData != null) {
        int ix = tl * 3 + td;
        ScopeData sd = dr.scopeData[ix];
        if (sd != null) {
          String prefix = sd.prefix;
          if (prefix != null) {
            sb.append(prefix);
            return sd.requiresDigitPrefix;
          }
        }
      }
      return false;
    }
docs: Append the appropriate prefix to the string builder, depending on whether and
  how a limit and direction are to be displayed.
  
  @param tl how and whether to display the time limit
  @param td how and whether to display the time direction
  @param sb the string builder to which to append the text
  @return true if a following digit will require a digit prefix