The query expression is a building block that can be assembled to define the final selection predicate for the query.
该查询表达式是一个构建块，可以通过组装它为查询定义最后的选择谓词。
2
That's the "TMC 2" in the regular expression toward the top of the block.
那是接近代码块顶部的正则表达式中的 “TMC 2”。
3
The while loop, as was the case with the if statement, supports an optional else clause containing a block of program statements executed when the expression is False.