Matt Martz

achmafooma

Moves the gallery shortcode styles to the head so it doesn’t break XHTML 
validation; allows disabling or modifying the default gallery styles.
By default when using the WordPress gallery, the styles are placed into the 
post content which breaks XHTML validation. This plugin moves the style into 
the head of the page using a look-ahead to determine if the [gallery] 
shortcode is used in any posts.
This plugin also gives you the option to modify the default gallery style 
CSS or disable the gallery styles entirely (so you can control it from your 
template CSS files).
This plugin uses ideas recommended in a patch located at 
https://trac.wordpress.org/attachment/ticket/6380/6380-style.diff
Special thanks to 
* The original author: Matt Martz, http://sivel.net 
* Serbo-Croatian (sr_RS) translation: Borisa Djuraskovic, http://www.webhostinghub.com 
* Spanish (es_ES) translation: Ogi Djuraskovic, http://www.webhostinghub.com/

Gallery Shortcode Style to Head

Moves the gallery shortcode styles to the head so it doesn't break XHTML validation; allows disabling or modifying the default gallery styles.

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  …

Gallery Shortcode Style to Head vs (x)html easy validator