(?x)applies the following effective flags to the remainder of the pattern: gmx x modifier: extended. Ignores unescaped whitespace and comments outside character classes
^start of line
Negated Character Class[^-]+ +matches at least one character outside the set below:
-the literal - (4510 / 558 / 2D16)
Comment: Capture everything not a dash
\s+any whitespace character, repeated at least once
-the literal - (4510 / 558 / 2D16)
\s+any whitespace character, repeated at least once
Comment: Match white space(s) dash white space(s)
(?1)calls group 1 as a subroutine
Comment: Capture everything not a dash
\.the literal . (4610 / 568 / 2E16)
mp3
the literal text mp3 (case sensitive) $end of line
g modifier: global. Finds all matches instead of stopping after the first
m modifier: multiline. Causes ^ and $ to match the start and end of each line, not only the start and end of the string