Simple: 

!/neither.*nor/ && /nor/

[download]

Complicated (and surely slower): 

/^(?:(?!neither).)*nor/

[download]

Update: Oops, they're not quite equivalent.
The first will match when no "neither" is found before the last "nor".
The second will match when no "neither" is found before the first "nor".

In reply to Re: regex, use of lookaround for whole word filtering by ikegami
in thread regex, use of lookaround for whole word filtering by yonatan

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