Non-Capturing Group(?:(?=\b(?:\p{Lu}\h+){2}\p{Lu})|\G(?!\A)) 1st Alternative(?=\b(?:\p{Lu}\h+){2}\p{Lu}) Positive Lookahead(?=\b(?:\p{Lu}\h+){2}\p{Lu}) \ban ASCII word boundary
Non-Capturing Group(?:\p{Lu}\h+){2} {2}repeats the group contents below exactly 2 times:
\p{Lu}an uppercase letter
\h+any horizontal whitespace character, repeated at least once
\p{Lu}an uppercase letter
\Gstart of current search
\p{Lu}an uppercase letter
\Kresets the starting point of the reported match. Any previously consumed characters are no longer included in the final match
\h+any horizontal whitespace character, repeated at least once
Positive Lookahead(?=\p{Lu}) \p{Lu}an uppercase letter
g modifier: global. Finds all matches instead of stopping after the first