regexp how to avoid replace in tag attributes

<?php
$strText = stripslashes(mysql_escape_string($row['text_data']));
/*added later to replace string*/
if(isset($_GET['searchChapWords'])){
	$searchChapWords = $_GET['searchChapWords'];
	$searchChapWordsArr = explode(" ", $searchChapWords);
	//print_r($searchChapWordsArr);
	# Where the good words go
		$bigWords = array();
		
		# Cycle through each word
		foreach ($searchChapWordsArr as $word) {
		  # if it's 4 chars or less
		  if (strlen($word) > 4 && !in_array($word,$bigWords)) {
			# add it to the small words
			$bigWords[] = $word;
		  }
		}
	for($a=0; $a<count($bigWords);$a++){
		$strText = preg_replace("/(".$bigWords[$a].")/i", "<span class=\"\" id=\"\" style=\" 						font-weight:bold;\">$1</span>", $strText);
		//echo $searchChapWordsArr[$a]."<br />";
	}
}
echo $strText."\n";
/**/
?>

PHP:

I want to avoid the preg_replace of the tag attributes. I notice the word font-weight is split because it's sorting the word eight.