code: private static final void addCaseMapping(UnicodeSet set, int result, StringBuilder full) {
          if(result >= 0) {
              if(result > UCaseProps.MAX_STRING_LENGTH) {
                  // add a single-code point case mapping
                  set.add(result);
              } else {
                  // add a string case mapping from full with length result
                  set.add(full.toString());
                  full.setLength(0);
              }
          }
          // result < 0: the code point mapped to itself, no need to add it
          // see UCaseProps
      }
docs: use str as a temporary string to avoid constructing one