To add a target like _blank

1- Go to administration inside text format (admin/config/content/formats)
and choose the format you want to allow target.

2- Activate the filter HTML Purifier (advanced)

3- at bottom of option there is a tab to configure html purifier, the second option is AllowedFrameTargets
in that field add the target you want to allow in this case: _blank (check the picture attachment).

4- go bottom of the page and save change.

5- Delete cache

SOme one can use it to create another documentation about HTML Purifier. I can delete it!

How to install the module:

PREREQUISITES: Make sure you check HTML Purifier and make sure that you
have fulfilled all of its requirements before running this. Specifically,
you'll need the PHP extension ctype (in almost all PHP distributions),
and it's nice to have dom and iconv.

* Place the htmlpurifier folder in your drupal modules directory.

HTML Purifier is a standards-compliant HTML filter library. It will not only remove all malicious code (better known as XSS) with a thoroughly audited, secure yet permissive whitelist, it will also make sure your documents are standards compliant, something only achievable with a comprehensive knowledge of W3C's specifications.