UUE file format information
Can someone provide me with a link to how a UUE file is laid out? I'm not looking for converters, but information on how a UUE file is formatted and why. For example, I see "begin 644 filename.ext" but other times the number is 666 or 600. I want to know why that is and more info about the specs.
It is with these kinds of questions that I can't get a good response from Google, because there are a billion pages talking about file extensions or converters.