[?&]
is one of
?
or
&
XYZ=
is just that exact text (case sensitive)
\\(
is the opening bracket character
(
. The
\\
is escaped by the compiler, so it is passing
\(
into the regex
[:alnum:]
is shorthand for
A-Za-z0-9
(no square brackets) which expands to
ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789
. Note that the
[]
is part of this expansion.
[[:alnum:]]
searches for
[A-Za-z0-9]
[[:alnum:]]*
searches for any number of
[[:alnum:]]
(see previous)
\\)
is the closing bracket character
)
. Again
\\
is escaped by the compiler, passing
\(
in as the regex
So, it is searching for
?XYZ=()
or
&XYZ=()