code: public final UnicodeSet remove(CharSequence s) {
          int cp = getSingleCP(s);
          if (cp < 0) {
              strings.remove(s.toString());
              pat = null;
          } else {
              remove(cp, cp);
          }
          return this;
      }
docs: Removes the specified string from this set if it is present.
  The set will not contain the specified string once the call
  returns.
  @param s the string to be removed
  @return this object, for chaining