How to use the symbols literally?

[JulyAn1234]

For example, I have this regex that works in Flex:
+|-|*|/|%|**|//|mod|÷

In flex the Backslash (for some reason this symbol is not showing once the issue is published) preceeding a character with a special meaning in a regex, makes said symbol literal. For example, in the regex above I literally mean a sequence of two asteriks ("**"). How can I do this here?

[Divide-By-0]

You can use my fork at https://zkregex.com/min_dfa and at https://github.com/Divide-By-0/dfa-toolbox! Waiting on merge still.