In XOOPS 2.3.3 (and previous versions I guess), a post or comment that has some Youtube video embed with Xoopscode "Youtube" won't pass HTML Validation.
I think this can be fixed modifying line 75 in the archive class/textsanitize/youtbe/youtube.php:
$code = "<object width='{$width}' height='{$height}'><param name='movie' value='{$src}'></param>" .
"<param name='wmode' value='transparent'></param>" .
"<embed src='{$src}' type='application/x-shockwave-flash' wmode='transparent' width='425' height='350'></embed>" . "</object>";
Changing it to, for example, this:
$code = "<object width='{$width}' height='{$height}' data='{$src}' type='application/x-shockwave-flash'>" .
"<param name='movie' value='{$src}'></param>" .
"<param name='wmode' value='transparent'></param>" .
"</object>";
Regards: Colossus