Sometimes double negation is difficult to understand ...

More than just sometimes, IMHO, but it's tolerable if taken in moderation. E.g., if you need a "digit boundary" assertion analogous to  \b in that it also matches at the start/end of a string, then  (?<! \d) and  (?! \d) are very attractive. Then  (?<! \d) \d{4} (?! \d) matches  '1234' 'x1234' '1234x' 'x1234x' but none of  '12345' 'x12345x' etc. Extend this to  (?<! \D) and  (?! \D) and you have a sometimes-useful double-negation asserting "non-digit boundary".

Give a man a fish:  <%-{-{-{-<

In reply to Re^7: Regex help \b & \Q by AnomalousMonk
in thread Regex help \b & \Q by Anonymous Monk

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