Given a String::  <vertical name="abc"><description> Replicant consists of Icon, Title1, Title2, Description, MOre Title, and More Hyperlink (minimum=0, maximum=10)</description><item min-allowed="1" max-allowed="20">

... I have tried using something like this

<item .(*)?><description>(.*)?</description><replicant (.*)?>
[download]

as search pattern but didnt succeed .

Well, of course something like that wouldn't succeed: the data sample has the "item" tag after the "description" tag, but the regex you tried has these tags the wrong way around. And why are you looking for a "replicant" tag that doesn't occur in the sample data?

Try putting <code> ... </code> tags around sample data and code snippets when you post or update a node, and try a solution that makes sense for the given data.