Special characters for filename

[chinyeungli]

The current spec allows the following symbols: "_", "-", "+", ".", "(", ")", "~", "[", "]", "{", "}"
https://github.com/nexB/aboutcode-toolkit/blob/develop/SPECIFICATION.rst#about-file-name

However, I am still able to generate ABOUT files with ! and @, but it fails when doing attrib.
Note that ! is likely not allowed in linux system, but @ seems is accepted in both linux and windows as filename
Should we allow more special characters for filename?

[DennisClark]

@chinyeungli I just saved a file on the Mac with filename = licenseref@example.png
and it saved with no problems
and I can open it and edit it with no problems.
So I am all in favor of allowing the @ character in an about-file-name.