Peadig

rel=”external” is now the XHTML valid version that informs search engine spiders that the link is external. However, using this does not open the link in a new window. target=”_blank” and target=”_new” does this, but is not XHTML valid.
This very simple plugin adds a small JS file to your header to let this happen!
<ul>
<li><a href="http://pleer.co.uk/wordpress/plugins/rel-external/" rel="nofollow ugc">rel=”external”</a> plugin homepage.</li>
<li>More <a href="http://pleer.co.uk/wordpress/plugins/" rel="nofollow ugc">WordPress Plugins</a>.</li>
<li><a href="http://pleer.co.uk/wordpress/plugins/facebook-comments/" rel="nofollow ugc">Facebook Comments</a> Plugin</li>
<li><a href="http://pleer.co.uk/wordpress/plugins/wp-twitter-feed/" rel="nofollow ugc">Twitter Feed</a> Plugin</li>
<li><a href="http://twitter.com/alexmossSEO" rel="nofollow ugc">Follow @alexmossSEO on Twitter</a>.</li>
<li><a href="http://alex-moss.co.uk/" rel="nofollow ugc">Alex Moss</a>.</li>
<li><a href="http://pleer.co.uk/" rel="nofollow ugc">Pleer SEO</a>.</li>
</ul>

rel=”external” in a New Window

Opens a new window with rel="external" instead of having to use target="_blank" or target="_new"

David Favor

This plugin fixes current HTML syntax errors raised due to how WordPress 
currently returns some links with rel=”category tag”.
Hopefully this plugin is temporary and WordPress will fix this problem.
At present it looks doubtful this will be fixed.
You can read more about this problem by 
[Searching WordPress for related discussions](https://www.google.com/search?q=”site:wordpress.org”+”category tag”+”rel”+”validation error”)…
Especially <a href="https://core.trac.wordpress.org/ticket/22095" rel="nofollow ugc">WordPress Ticket #22095</a> 
talks about what has been fixed (2 problems) and what has been 
deferred indefinitely (1 problem).
<h4>Like This Plugin?</h4>
This plugin is provided for free.
If you like using it + like to say thanks…
Buy a copy of my <a href="http://DavidFavor.com/bb" rel="nofollow ugc">“Beautiful Business”</a> Kindle Book and 
post an Amazon Review of what you enjoyed most.
<h4>Why This Plugin is Essential</h4>
The following is purely my opinion about this matter.
In most cases, your best option when having Web development work done is to make your 
payment contingent on the following checklist… meaning you only pay 
for your Web development after all checklist items are 100% met. No exceptions.
Some diehards in the audience may say Validator code lags standards. True. And 
I’d prefer adhering to the current Validator code rather than constantly 
trying to determine which errors and warnings are acceptable and which are real.
Your Web development checklist:
<ul>
<li><a href="http://Validator.w3.org/" rel="nofollow ugc">W3C HTML Validator</a> – 100% clean HTML syntax validation. Zero errors. 
Zero warnings. No exceptions, save one. The single exception is one warning, 
which the validator currently emits if you use an HTML5 Doctype ().</li>
<li><a href="http://Jigsaw.w3.org/css-validator/" rel="nofollow ugc">W3C CSS Validator</a> – 100% clean CSS syntax validation. Zero errors. 
Zero warnings. No exceptions.</li>
<li><a href="http://WebPageTest.org" rel="nofollow ugc">Web Page Test</a> – A score in ever category. No exceptions, save one. Do yourself 
a favor and skip using a CDN, unless you’re serving huge video files off your site. 
Even then, unless your CDN supports true streaming (meaning you can move the scrubber 
bar and the video playback position tracks + changes correctly) you’re better off hiring 
some to correctly tool your site. Follow this checklist and a CDN will rarely give you 
any measurable speed increase.</li>
<li><a href="https://developers.google.com/speed/pagespeed/insights/" rel="nofollow ugc">Google PageSpeed</a> – 100 out of 100 PageSpeed Score. 
In other words, all tests pass. No exceptions.</li>
</ul>
Having “No exceptions” in each case will also require you use a Hosting Company run by 
Wicked Smart Uber Geeks. I’ve yet to find any company who can tune up a Web server to 
run as fast as I tune mine, so I run my own “Iron” (servers which I admin personally).
This said, you may have some exceptions. You’ll have to determine which are acceptable for you.
For me, “No exceptions” is mandatory.
Enough rambling.

rel=”external” in a New Window vs WordPress Fix HTML5 Validation