是一类不依赖于标准字符串的php日期格式。

The 'r' is a generic PHP date format that does not rely on translated strings.

youdao

这可以确保在查询中使用日期比较，而不是标准的字符串比较。

This ensures that the date comparison is used in the query, rather than standard string comparison.

youdao

即使一个标准的旧式字符串值也至少有255个字符。

Even a standard old school string value has at least 255 characters.

youdao

You're going to get a chance to explore them, and you'll see not only are there the standard numerics for strings, there are things like length or plus or other things you can do with them.

以后你们还会学到更多，你会学到字符串,不仅仅能运用标准数值运算，你还可以对他们求长度,或者加上其他的东西。

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