Each time a pointer field in an object in the heap is modified, the corresponding bit in the card map for that card is set.
每次修改堆中对象中的指针字段时，就在卡片映射中设置对应那张卡片的相应位。
3
This header tells you quite a bit about your server, but never fear: Web servers can quite commonly have this information sanitized or modified to a particular organization's tastes.