How can I replace to sub strings (html code)?

[Betty_S]

How can I replace to sub strings (html code)?
Hi,
I have that:

$x = 	". . .
	<div class="somecalss"> . . .
	. . .
	. . .
	</div>
	. . .";
$y = "some html code";.

How can I replace the <div> part in $x with $y?
I now that I can do it with RegEx (regular expression) and str_replace but how to define a RegEx?
How can do that?
Is it something like that:

 
$r='/\'<div class="somecalss">+.+'</div>''/\';

And then what?

Thanks.

[bradgrafelman]

So you want to find a <div> element and replace everything inside that element with some variable $y ? Try a pattern like this:

$pattern = '@<div class="someclass">.*?</div>@s';

and use a function such as [man]preg_replace/man.