s      # substitute
/      # begin search sequence
<      # find a literal <
(?!    # negative lookahead ie find a < not followed by
\/*    # 0 or more / chars
[bi]   # then either a 'b' or and 'i' char
>      # then a literal >
)      # end of negative lookahead
.*?    # 0 or more of any characters, non greedy ie minimal
>      # a literal >
/x/    # replacement sequence is a literal 'x' char
g      # do all occurences