It's very likely I could be wrong, I haven't tested it, but I think it would work.

my $section = '';
foreach (@m) {
  if (
    /^        #match the start of the line
      \s*    #match 0 or more whitespace characters grab as many as we
+ can
      (        #start captureing
        [\w\s]*?    #match 0 or more word or whitespace, grab as _few_
+ as posible
      )        #end capture
      \s*    #match 0 or more whitespace characters
      :        #until we reach the a colon
    /x         #x added for the comments
    &&         #if the match fails we don't bother checking $1
    $1) {    #check if we captured any thing if there was only whitesp
+ace before the colon we won't have captured any thing
    $section = $1;    #if we actualy found a section label save it
  }
  #$section should now be set to the last section label we found.
  if ($section eq '...') {
...
}
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