Modified wr2x_srcset_rewrite function for Retina 2x WordPress plugin that fixes the [partial] stripping of HTML tags when using the HTML srcset option. This is the all-new function that follows the HTML rewrite's method of adding the retina image's code.

gistfile1.txt

function wr2x_srcset_rewrite( $buffer ) {
	if ( !isset( $buffer ) || trim( $buffer ) === '' )
		return $buffer;
	$doc = new DOMDocument();
	@$doc->loadHTML( $buffer ); // = ($doc->strictErrorChecking = false;)
	$imageTags = $doc->getElementsByTagName('img');
	foreach ( $imageTags as $tag ) {
		$img_info = parse_url( $tag->getAttribute('src') );
		$img_pathinfo = ltrim( $img_info['path'], '/' );
		$filepath = trailingslashit( ABSPATH ) . $img_pathinfo;
		$potential_retina = wr2x_get_retina( $filepath );
		if ( $potential_retina != null ) {
			wr2x_log( "Add srcset:  " . $potential_retina . ' 2x' );
			$retina_pathinfo = ltrim( str_replace( ABSPATH, "", $potential_retina ), '/' );
			$retina_url = trailingslashit( get_site_url() ) . $retina_pathinfo;
			$img_url = trailingslashit( get_site_url() ) . $img_pathinfo;
			$buffer = str_replace( 'src="'.$img_url.'"', 'src="'.$img_url.'" srcset="'.$retina_url.' 2x"', $buffer );
		}
	}
	return $buffer;
}