Pop a -? into your [regexp] and it will find the minus sign if it exists and carry on working regardless if it doesn’t. There’s a regexp tutorial on my webpage which I hope you find helpful, if you click on my name next to this post it will point you there. Here’s a little example patch:
-- Pasted Max Patch, click to expand. --
Copy all of the following text. Then, in Max, select New From Clipboard.