How to replace text except when it's between two tags in PHP?

I have a statement replacement to do in php (using str_replace or something else). I have this sentence:

the sun is yellow when the <wrong>red sun is not 开发者_运维问答yellow</wrong>

I want this:

the apple is yellow when the <wrong>red sun is not yellow</wrong>

So I need to replace a word, except between two specific tags (<wrongand </wrong>). How to do that with str_replace or using a regex?

If the string is small, why not use explode() to explode it at the tags, and replace the strings in required fragments, and then rejoin it ? Or try DomDocument :

<?php

$str = "the sun is yellow when the <wrong> This is also red sun not yellow red sun is not yellow some words </wrong> and here is 
yellow sun outside <wrong> , now yellow sun inside </wrong>";

$origArr = array("sun");
$replaceArr = array("apple");
$str = str_replace($origArr,$replaceArr,$str);

$domElem = new DOMDocument();
$domElem->loadXML("<temp_tag>".$str."</temp_tag>");

$nodes = $domElem->getElementsByTagName('wrong');


$index = 0;
while($nodes->item($index)->nodeValue)
  {
    $nodes->item($index)->nodeValue = str_replace($replaceArr,$origArr,$nodes->item($index)->nodeValue);
    $index++;
  }

echo $domElem->saveHTML();

/* remove the <temp_tags> ....*/

?>

See it here: http://codepad.org/T5o3shB4

the difference is sun -> apple in the second word. for that example str_replace('sun', 'apple', $text, 1) will do just the first one