The .. and ... operators test for a start and end pattern. The 2 dot version tests both patterns on the same line once it finds the first one. The 3 dot version doesn't look for the end pattern until the line after finding the start.

I've used it like this to extract some part of a logfile:

open my $fh, '<', $log_file or croak "Couldn't open '$log_file'";
    while (<$fh>) {
        push( @session, $_ ) if (/^\d\d\/\d\d\/\d\d.+Start of Logging$
+/m ... /^\d\d\/\d\d\/\d\d.+End of Logging$/m)
    }
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