\ba Unicode word boundary
Negative Lookahead(?!test) testthe literal text test (case sensitive) \w+?a Unicode word character, repeated at least once
\.?optionally matches the literal . (4610 / 568 / 2E16)
\w+a Unicode word character, repeated at least once
@gmailthe literal text @gmail (case sensitive) \.the literal . (4610 / 568 / 2E16)
comthe literal text com (case sensitive) 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