edik

If FacadeX is active, the public WordPress sites are sent with the xhtml mime type. The internal sites like the administration panel and the login screen, which have many xhtml syntax errors, are still sent with the standard mime type.
You must ensure that your public sites have valid XHTML, otherwise you will get parsing errors in your browser.

FacadeX

Sends public sites with the XHTML mime type. The internal sites, which have many XHTML errors, are still sent with the HTML mime type.

SaltwaterC

XVE (XVE Various Embed) is a simple yet powerful way to add media content to your WordPress blog. It is a drop-in replacement for my old XHTML Video Embed plug-in, while it aims to continue the original support.
The plug-in is self documented, so there’s the point where you may want to start. The help is integrated into the WordPress help system. If you’re looking for it, it’s into the above menu, the ‘Help’ item. For some of you, this isn’t so obvious as the Help system is kinda new.
New features and support requests are honored better if you open a <a href="https://github.com/SaltwaterC/XVE-Various-Embed" title="GitHub" rel="nofollow ugc">ticket on GitHub</a> where this plug-in is actually hosted.
Supported video services: youtube.com (youtu.be URLs as well), metacafe.com, dailymotion.com, revver.com, spike.com, vimeo.com, livestream.com, capped.tv, trilulilu.ro, 220.ro, collegehumor.com, myvideo.de, snotr.com, gametrailers.com, blip.tv
Supported audio services: trilulilu.ro, 220.ro
Supported image services: trilulilu.ro
It also supports generic SWF / FLV (MP4) embedding.
For the FLV (MP4) embedding, there are three provided players: Flowplayer, FLV Player, and JW Player. You may change them on the fly without the need to change the embed code.

XVE Various Embed

XVE (XVE Various Embed) is a simple yet powerful way to add media content to your WordPress blog.

FacadeX vs XVE Various Embed