Invalid usage of rel="_blank" in HTML5 links

In the XWiki Syntax guide, there is:

rel: An optional parameter that allows to open link target in new window. Example: rel="__blank"

So if you do, in XWiki Enterprise:

[[Blog>>Blog.WebHome||rel="__blank"]]}}

the HTML5 generated code is

<a rel="__blank" href="/xwiki/bin/view/Blog/">Blog</a>

This code is invalid because "__blank" is not an authorized value for the attribute "rel" in HTML5 (contrary to XHTML 1.0).

In HTML5, target="_blank" is perfectly valid, so there is no reason to use the "rel" workaround anymore.