The prefix can contain numbers, as can the suffix. The idea is to increment one number to generate a list, e.g.

01-file-01.html
01-file-02.html
01-file-03.html
...
[download]

Only one number is ever going to form the basis for the list so the other numbers in a filename should be part of either the prefix or the suffix. I get the feeling I'm not explaining this very well...

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Grant me the wisdom to shut my mouth when I don't know what I'm talking about.