Negative number highlighting
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Negative numbers are not recognized/highlighted as numbers for me with Notepad++v7.8.6 (64-bit) on Windows 10.

The blue highlighting is correct for numbers.
Re: user-defined syntax highlighting -
If, for example, I define
(and)as operators I do get the following
How did you define the brackets, as delimiters and if so have you allowed nesting with numbers?