^start of string
a:the literal text a: (case sensitive) \d+a digit, repeated at least once
+repeats the group contents below at least once:
i:the literal text i: (case sensitive) \d+a digit, repeated at least once
;the literal ; (5910 / 738 / 3B16)
}the literal } (12510 / 1758 / 7D16)
$end of string, or before its final line terminator