code: public final int tolower(int c) {
          int props=trie.get(c);
          if(!propsHasException(props)) {
              if(getTypeFromProps(props)>=UPPER) {
                  c+=getDelta(props);
              }
          } else {
              int excOffset=getExceptionsOffset(props);
              int excWord=exceptions.charAt(excOffset++);
              if(hasSlot(excWord, EXC_LOWER)) {
                  c=getSlotValue(excWord, EXC_LOWER, excOffset);
              }
          }
          return c;
      }
docs: simple case mappings ------------------------------------------------ ***