A domain determines the parser that is used when parsing and serializing the message.
域确定了在解析和序列化该消息时使用的解析器。

Semantic actions may be attached to any expression at any level within the parser hierarchy.
语义动作可以挂接到分析器内任意层次的任意表达式上。

The most complex part of the compound class parser is the interpretation of logical conjunctions and disjunctions.
复合类解析器最复杂的部分在于逻辑合取和析取的解释。