What does the cryptic crossword clue "Ace regiment dispersed in event at Doncaster, maybe (4,7)" mean?

The wordplay uses an anagram. anagram of ACE + REGIMENT = RACEMEETING The answer is RACEMEETING.

Ace regiment dispersed in event at Doncaster, maybe (4,7)

Daily Mail Cryptic #17120 | 29 Across | 2023-06-15 flower