^start of line
#the literal # (3510 / 438 / 2316)
*the literal * (4210 / 528 / 2A16)
\sany whitespace character
Group 1(\[item:(.+?)\]|(.+?)) 1st Alternative\[item:(.+?)\] \[the literal [ (9110 / 1338 / 5B16)
item:the literal text item: (case insensitive) .+?any character (except for line terminators), repeated at least once
\]the literal ] (9310 / 1358 / 5D16)
.+?any character (except for line terminators), repeated at least once
\sany whitespace character
\[the literal [ (9110 / 1338 / 5B16)
.+any character (except for line terminators), repeated at least once
$end of line
g modifier: global. Finds all matches instead of stopping after the first
i modifier: insensitive. Matches without distinguishing uppercase and lowercase letters
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string