Brace expansion is not specific to pathname matching. I've shown you: type

echo a{1..3}
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you get

a1 a2 a3
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even if such files do not exist.

echo > a1; ls a{1..3}
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prints

ls: a2: No such file or directory
ls: a3: No such file or directory
a1
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There is a filename matching feature too, in bash it looks like this:

shopt -s extglob 
echo a@(1|2|3)
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is really similar to the friendly echo a[1-3], it prints

a1
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if a1 exists but the other files don't. (Don't ask me how it works in zsh.) There is no numeric range variant of this though.