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.

iThemes

Chris Wiegman

Selecting “Open link in a new window” in the builtin WordPress WYSIWYG editor breack XHTML strict compliance by adding the attribute target=”_blank” to anchor tags. This plugin fixes the problem by replacing the target attribute with a common class attribute and then using a simple jquery script to open the link in a new window. This method allows for correct validation using XHTML 1.0 Strict.
<h3>License</h3>
Released under the terms of the GNU General Public License.

Replace Anchor Target

Replaces target="_blank" attribute for XHTML Strict compliance.

FacadeX vs Replace Anchor Target