^start of line
(?i)applies the following effective flags to the remainder of the pattern: gmi i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
.*any character (except for line terminators), repeated any number of times
Positive Lookahead(?=\w*?(.)\1\1) \w*?any word character, repeated any number of times
.any character (except for line terminators)
\1the text saved by group 1
\1the text saved by group 1
\ban ASCII word boundary
m+the literal m (10910 / 1558 / 6D16) (case insensitive), repeated at least once
u+the literal u (11710 / 1658 / 7516) (case insensitive), repeated at least once
t+the literal t (11610 / 1648 / 7416) (case insensitive), repeated at least once
e+the literal e (10110 / 1458 / 6516) (case insensitive), repeated at least once
x+the literal x (12010 / 1708 / 7816) (case insensitive), repeated at least once
\ban ASCII word boundary
.*any character (except for line terminators), repeated any number of times
$end of line
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string