/^\.(\w+).*$\t+\.\w+\W+(\w+).*$/m
[download]

So you're looking for something like this, I think:

.somewords any amount of garbage till a suposed end of line
[some number of tabs].nomatchwords matchedwords garbage to eol
[download]

I'm going on this assumption since I have NO real example of your test data.

#!/usr/local/bin/perl -w
use strict;
$|++;

$/="\n.";
while ( <DATA> ) {
  print join ' ', /^\.?(\w+).+\n\t+\.\w+\W+(\w+)/;
  print "\n";
}


__DATA__
.this is a line
        .and this is another line
.again, a line.
                .Yet another line
[download]

I hope this helps.

--
Casey