code: public String format(long number, String ruleSet) throws IllegalArgumentException {
          if (ruleSet.startsWith("%%")) {
              throw new IllegalArgumentException("Can't use internal rule set");
          }
          return adjustForContext(format(number, findRuleSet(ruleSet)));
      }
docs: Formats the specified number according to the specified rule set.
  (If the specified rule set specifies a master ["x.0"] rule, this function
  ignores it.  Convert the number to a double first if you ned it.)  This
  function preserves all the precision in the long-- it doesn't convert it
  to a double.
  @param number The number to format.
  @param ruleSet The name of the rule set to format the number with.
  This must be the name of a valid public rule set for this formatter.
  @return A textual representation of the number.