is there a meaningful difference between (?![a-z]) and (?=[^a-z])? is the former recommended?

Yes, they're different regular expression patterns that match different things. (?![a-z]) asserts "not followed by any of the characters from 'a' through 'z', which includes not being followed by any character." (?=[^a-z]) asserts "followed by a single character that is not any of the characters from 'a' through 'z'." The former is a negative assertion; the latter is a positive assertion.

In your case, (?![a-z]) is what you would want to use.

[PerlMonks posting tip: Enclose Perl code in <code></code> tags, even code within paragraphs.]

UPDATE: Removed color.

In reply to Re^3: Defining Characters in Word Boundary? by Jim
in thread Defining Characters in Word Boundary? by iaw4

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