Regular Expressions 101

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/
\b(?!всемирный)\wмир\w
/
gu
\b assert position at a word boundary: (^\w|\w$|\W\w|\w\W)
Negative Lookahead
(?!всемирный)
Assert that the Regex below does not match
всемирный matches the characters всемирный literally (case sensitive)
\w
match any word character in any script (equivalent to [\p{L}\p{N}_])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
мир matches the characters мир literally (case sensitive)
\w
match any word character in any script (equivalent to [\p{L}\p{N}_])
* matches the previous token between zero and unlimited times, as many times as possible, giving back as needed (greedy)
Global pattern flags
g modifier: global. All matches (don't return after first match)
u modifier: unicode. Pattern strings are treated as UTF-16. Also causes escape sequences to match unicode characters
Your regular expression does not match the subject string.Try launching the debugger to find out why.

Regular Expression
No Match

/
/
gu

Test String