The RFC moves on to coverage of content constructs with sections 4.5 and 4.6, which offer very sensible advice on when to use processing instructions and comments.
RFC在4.5和4.6节讨论内容结构，就何时使用处理指令和注释提供了非常合理的建议。
A node can contain text, attributes, other nodes (hence, the hierarchical nature of XML), and a few other specialized things (such as processing instructions and comments).
节点可以包含文本、属性、其他节点(因此形成XML的层次结构)以及其他一些特殊的东西(比如处理指令和注释)。
It expands entities and ignores processing instructions and comments.
可以扩充实体并忽略处理指示和注解。
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