本文通过铁路图比喻解析了一种特殊的语法结构。进入图表从左侧开始，在第一个开关处没有选择左右的选项，类似于铁路开关只能沿固定轨道前进。右侧的开关允许从左而来的流量选择不同的路径，从而结束或重复语法规则。此图定义了空白字符可以由任意数量的空格、制表符、行尾或注释组成。
As a "railroad diagram", this has some properties in common with a railroad track.
Upon entering the diagram from the left, when arriving at the first switch, there is no option of going left or right. Just like a railroad switch, the diagram switch has two converging tracks, but no way to pass from one of those to the other.
The switch on the right hand side however, with traffic arriving from the left, provides the options of following either of the diverging routes, effectively ending or repeating the syntax rule.
Thus the diagram defines instances of whitespace to be composed of any positive number of spaces, tabs, line ends, or comments.
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