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.

Nikoya

Check the doctype validity using W3c validator (html , xhtml , … ) when creating or updating page / post / custom post type and show the result in backend 
It show the result in back-end in sortable column, a link is add to the w3c for all file to help you to correct html error.
Very easy to see if a post / page is valid or not.
This plugin can check the W3C validity of your page / post or custom post type even if the site is not accessible from the Internet (if you work on local system for example)

(x)html easy validator

Check the doctype validity using W3c validator (html , xhtml , ... ) when creating or updating  page / post / custom post type and show the result in  …

Replace Anchor Target vs (x)html easy validator