Ruby regexp should exclude "125af" substrings
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I have the following regexp:

    /^(\d{1,11})((?:(?:c?o|co?).*)?.*)$/i

that matches strings like:

    125******* or 125co****** or 125CO*******

I would like to exclude substrings that begin with:

    125af***** or 125AF****** or 125f****** or 125AF********

Thanks in advance