.NET Regex Error: [x-y] range in reverse order

Question

I am creating a Regex and so far I did this and tried it,

 ^([0][1-9]|1[0-2])[/-.]

and I get the following error.

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Answer 1

Not a bug. Inside a character class (denoted by […]) the - character must be first (some flavours allow first or last, I believe) if it is to be included as a literal. Otherwise it is expected to denote a range, such as 0-9 or A-Z or even /-..

The problem is that according to Unicode, the . comes before the /, so the range is interpreted to be backward, equivalent to specifying a range 7-4.

If you used [.-/], I would not expect a parse exception, but you wouldn't get the results you expected.