Hello,   I am trying to write a regex to match just with B2 and B3   String content = "aaaaaB1aaaaaXaaaaaB2aaaaaB3aaaaZaaaB4aaaa";   String regex = "(B[\\d]{1}?);    //this group matches with all B1, B2, B3 and B4  I would need to delimit the matching between the 'X' and the ...