Not sure what you mean by it being missing. The binary flag is mentioned. They just don't list r and rb as different modes because it's unnecessary.
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Windows offers a text-mode translation flag ('t') which will transparently translate \n to \r\n when working with the file. In contrast, you can also use 'b' to force binary mode, which will not translate your data. To use these flags, specify either 'b' or 't' as the last character of the mode parameter.