Negative Lookbehind(?<![^\W_]) Negated Character Class[^\W_] \Wany non-word character
_the literal _ (9510 / 1378 / 5F16)
nthe literal n (11010 / 1568 / 6E16) (case insensitive)
Non-Capturing Group(?:r?[_.]|umero_?) r?optionally matches the literal r (11410 / 1628 / 7216) (case insensitive)
_the literal _ (9510 / 1378 / 5F16)
.the literal . (4610 / 568 / 2E16)
umerothe literal text umero (case insensitive) _?optionally matches the literal _ (9510 / 1378 / 5F16)
\s*any whitespace character, repeated any number of times
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
\d+a digit, repeated at least once
g modifier: global. Finds all matches instead of stopping after the first
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters