使用h1和h2这样的实义标签来按照逻辑关系组织内容，有助于形成可访问性，因为读者总是习惯在阅读文字前先扫描标题。
Organizing content logically using meaningful headings such as h1 and h2 creates affordance, because readers habitually scan headings before reading the text.
一个编译过的文字数字或是在记忆体中数字的表示法是实作自订的。
The representation of a number as a compiled literal or in memory is implementation dependent.
标示一个文字输入行结束的方法是实作自订的。
The method of indicating the end of an input line of text is implementation defined.
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