D:\tmp\pm>perl -Mre=debug -E"'aaaa' =~/a*a*b/" Compiling REx "a*a*b" synthetic stclass "ANYOF[ab]". Final program: 1: STAR (4) 2: EXACT (0) 4: STAR (7) 5: EXACT (0) 7: EXACT (9) 9: END (0) floating "b" at 0..9223372036854775807 (checking floating) stclass ANYOF[ab] min len 1 Matching REx "a*a*b" against "aaaa" Intuit: trying to determine minimum start position... doing 'check' fbm scan, [0..4] gave -1 Did not find floating substr "b"... Match rejected by optimizer Freeing REx: "a*a*b"