code: public final UnicodeSet addAll(CharSequence s) {
          checkFrozen();
          int cp;
          for (int i = 0; i < s.length(); i += UTF16.getCharCount(cp)) {
              cp = UTF16.charAt(s, i);
              add_unchecked(cp, cp);
          }
          return this;
      }
docs: Adds each of the characters in this string to the set. Thus "ch" =&gt; {"c", "h"}
  If this set already any particular character, it has no effect on that character.
  @param s the source string
  @return this object, for chaining