(?m)applies the following effective flags to the remainder of the pattern: gm m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string
^start of line
.+any character (except for line terminators), repeated at least once
\na line-feed (newline) character (ASCII 10)
.+any character (except for line terminators), repeated at least once
\na line-feed (newline) character (ASCII 10)
.+any character (except for line terminators), repeated at least once
g modifier: global. Finds all matches instead of stopping after the first