Convert plain HTML to XHTML

Below is the example of converting from plain HTML to XHTML.

<?php 
/** 
  * Take a look at the Remark-Lines of the function-header 
  *  
  * function autoAdjustToXHMTL($string) 
  *  
  * Tries to make out of the given string a xhtml-compatible string, 
  * that means that the return-string could be wrapped within a xml. 
  * 
  * Example: $string = "<big><I>something<br></big> blabla" 
  *          return = "<big><i>something><br /></i></big> blabla" 
  * 
  * As you can see, the folowing will be changed: 
  *  - converted "<I>" to "<i>", as all html-nodes will be converted to lowercase 
  *  - converted "<br>" to "<br />" to make br xhtml-conform (same would be done with "img") 
  *  - the closing of "</big>" will have do an implicite closing of "<i>" because <big> surrounds "<i>" 
  * 
  * Beware: the output-string is not the most beautiful code possible but hopefully xhtml-conform 
  * 
  * @param string: input string, html-style (as a browser should like it) 
  * @return: xhtml-compatible string 
  * 
  * Version 
  * V1.0, 20090721, rene@pilz.cc, initial-version 
  * 
  * Released under the terms of BSD (http://en.wikipedia.org/wiki/BSD_licenses) 
*/ 
function autoAdjustToXHTML($string)
{ 
	$returnString=""; 
	$string=trim($string); 
	$elementStack=array(); 
	$stackPoint=0; 
	while ($string!="") { 
		$pos=strpos($string,"<"); 
		if ($pos===false) { 
			// no "<" found, return full string and exit while 
			$returnString.=$string;     
			break; 
		} 

		// copy anythink up to the "<" into return string and reduce string 
		$returnString.=substr($string,0,$pos); 
		$string=trim(substr($string,$pos+1)); 

		$tagName=""; 
		// examine tag-name 
		$i=0; $c=""; 
		for (;$i<strlen($string);$i++) { 
			$c=substr($string,$i,1); 
			if (strpos(";<",$c)!==false) continue;    // some chars we ignore 
			if ($c==" "|| $c==">") break; 
			$tagName.=$c; 
		} 

		$tagName=strtolower($tagName);    // convert uppercase  

		// is there a closing tag? 
		if (substr($tagName,0,1)=="/") { 
			// search for the closing ">" and ignore all before 
			$pos=strpos($string,">"); 
			if ($pos===false) $pos=strlen($string); 
			$string=substr($string,$pos+1); 
			// close as many tags up to the given tag 
			while ($stackPoint>0) { 
				 $stackPoint--; 
				 $stackElement=$elementStack[$stackPoint]; 
				 $returnString.="</".$stackElement.">"; 
				 if ($stackElement==$tagName) break;    // nothing more to do in this while 
			} 
			continue;    // this element-Processing is finished so far, continue at 'while ($string!="") {' 
		} 

		// if we are here, we are within a tag (opening tag) 

		// Push tag on stack 
		$elementStack[$stackPoint]=$tagName; 
		$stackPoint++; 

		// add tag to returnString 
		$returnString.="<$tagName "; 

		// search up to ">" 
		$inApo=false;    // within Apostrophes (" or ') 
		$fakeApo=false; 
		$apoChar=""; 
		for (;$i<strlen($string);$i++) { 
			$c=substr($string,$i,1); 
			if ($fakeApo && strpos(" 	",$c)) { 
				 $fakeApo=false; 
				 $returnString.='"'; 
			} 
			if (!$inApo && !$fakeApo && $c=='=' && !strpos(" 	'"",substr($string,$i+1,1))) { 
				 echo "test2=".substr($string,$i+1,1)."---"; 
				 $fakeApo=true; 
				 $returnString.='="'; 
				 $c=""; 
			} 
			if ($c==$apoChar && $inApo) { $inApo=false; $returnString.=$c." "; $c=""; } 
			if ($inApo && $c=="&" && strpos(substr($string,$i).";",";")>5) $c="&amp;"; 
			else if (($c=="'" || $c=='"') && !$inApo) { $inApo=true; $apoChar=$c; } 
			if ($c==">") break; 
			$returnString.=$c; 
		} 

		// new $string is the rest 
		$string=substr($string,$i+1); 
		$returnString=trim($returnString); 

		// check if this has a "/>" at the end 
		$endSlash=(substr($returnString,strlen($returnString)-1)=="/"); 

		// some elements must have a "/" at the end --> Fake it if needed 
		if (($tagName=="br" || $tagName=="img") && !$endSlash) {  
			$returnString.="/";  
			$endSlash=true; 
		} 

		// check if it is a remark-line (<!-- --> trade this as with-endSlash-Tag) 
		if (substr($tagName,0,3)=="!--") { 
			$returnString=trim($returnString); 
			if (substr($returnString,strlen($returnString)-2)!="--") $returnString.=" --"; // make sure remark-line ends with "-->" 
			$endSlash=true; 
		} 

		// again, do we have a end-slash? (or a faked one?) 
		if ($endSlash) $stackPoint--;    // just remove element from stack 

		// and now add the closing ">" 
		$returnString.=">"; 
	} 

	// ok, we are allmost finish, just clean up the elementStack (from last to first) 
	while ($stackPoint>0) { 
		$stackPoint--; 
		$returnString.="</".$elementStack[$stackPoint].">"; 
	} 
	return $returnString; 
} 
php?>