\ba Unicode word boundary
\w{1,3}a Unicode word character, repeated between 1 and 3 times
Positive Lookahead(?=\s|$) \sa Unicode whitespace character
\s*a Unicode whitespace character, repeated any number of times
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