Regular expressions can be complicated, not that one is pretty simple:
A fixed string "big bro"
Followed by
Any of the characters between the '[' and ']', repeated zero or more times.
The characters include all alphanumeric letters and digits, plus a range of special characters including the Unicode alpha characters (the "\p{L}" part)
So "big bro" will match, as will "big broX", "big bro9", and "big bro***" but "big bro***%***" with only match the "big bro***" part.
It you are goign to play with Regexes, then Get a copy of
Expresso[
^] - it's free, and it examines and generates Regular expressions.