Using DOMDocument to Modify HTML with PHP

// Formats post content for SSL
function format_post_content($content =   ) {
  $document = new DOMDocument();
  // Ensure UTF-8 is respected by using  mb_convert_encoding 
  $document->loadHTML(mb_convert_encoding($content,  HTML-ENTITIES ,  UTF-8 ));
  
  $tags = $document->getElementsByTagName( img );
  foreach ($tags as $tag) {
    $tag->setAttribute( src , 
      str_replace( http://davidwalsh.name , 
                   https://davidwalsh.name , 
                  $tag->getAttribute( src )
      )
    );
  }
  return $document->saveHTML();
}