^start of string
Group 1((00|\+)39[. ]??)?? ??repeats the group contents below at most once:
\+the literal + (4310 / 538 / 2B16)
??matches at most one character from the set below:
.the literal . (4610 / 568 / 2E16)
the literal (3210 / 408 / 2016)
3the literal 3 (5110 / 638 / 3316)
\d{2}a digit, repeated exactly 2 times
??matches at most one character from the set below:
.the literal . (4610 / 568 / 2E16)
the literal (3210 / 408 / 2016)
\d{6,7}a digit, repeated between 6 and 7 times
$end of string, or before its final line terminator