Unfortunately, like all quirks, bugs, and undocumented features, there was no guarantee it would be the same on subsequent releases. Microsoft Corp 1981-1995. Using choice to extract individual characters will work on all DOS versions. We need extra delimiters to separate the 1 and 5 from the brackets. Notice I used equals signs.
Most people use semicolons.
No real difference. Choice allows you to specify a prompt. You just add it to the end of the choice line and it shows up at the beginning of the output. But we will use the prompt as a way to get a batch file name at the beginning of the line. For increased readability, you should replace it with a space.