HTML to XHTML and reverse

function remSpecialChars($string) {
	$string = stripslashes($string);
	$string = eregi_replace("'","'",$string);
	$string = eregi_replace('"','"',$string);
	$string = eregi_replace('?','-',$string);
	$string = eregi_replace('?','’',$string);
	return $string;
}

function addSpecialChars($string, $noQuotes = FALSE) {
	$string = eregi_replace("&","&",$string);
	if (!$noQuotes) $string = eregi_replace("'","'",$string);
	$string = eregi_replace('"','"',$string);
	$string = eregi_replace('<','<',$string);
	$string = eregi_replace('>','>',$string);
	$string = eregi_replace(' ',' ',$string);
	return $string;
}