^start of line
\w{3,}any word character, repeated at least 3 times
\s+any whitespace character, repeated at least once
Non-Capturing Group(?:\w\s+)? ?repeats the group contents below at most once:
\wany word character
\s+any whitespace character, repeated at least once
\w{3,}any word character, repeated at least 3 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
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters