I've read that.. I understand I'm not a perl master, but if you know the solution, please, tell me where I'm not right.. 
$x = "<tr><td>1</td><td>2</td><td><font>3</font></td><td>4</td><tr>";

$x =~ s{<td>(?!<td>)3(?!</td>)</td>}{<td>($1)a($2)</td>}; 
print $x;

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It does not work... are there any ideas?

Update

deep posts does not appear for some reasons.. I'll post again in the top-level:

you see, I met such problem not with html only... this is a general question. I'm pretty sure there must exist some regex to solve the problem, but my knowledge is too small. But, nevertheless, thanks)

Maybe, someone other knows any regex solutions?

In reply to Re^2: regex: something...(!something)...something by aaaone
in thread regex: something...(!something)...something by aaaone

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