Those characters that do not map will be substituted by a reservedcode point.
那些没有映射的字符将通过预留的代码点来代替。
2
Every code page has reserved at least one code point for substitution.
每一个代码页至少预留了一个代码点，以便进行替代。
3
As only 27 tokens are available for elements -- 5 bits, with the values 0 through 4 being reserved -- complex vocabularies need to be multiplexed by organizing token sets into separate code pages.