#1936392: Configure CKEditor's "Advanced Content Filter" (ACF) to match Drupal's text filters settings ensured that ACF was optimally configured: so that it perfectly matches the restrictions by Drupal's text filters.
However, Drupal's text filters need to have the capability to blacklist attributes (filter_html disallows style and on* attributes on all tags). That's why a _ACF_HACK_to_support_blacklisted_attributes function was added to hack in a temporary work-around.
Once http://dev.ckeditor.com/ticket/10276 is fixed, we can remove that hack, and update Internal::generateAllowedContentSetting() to communicate our blacklist to CKEditor in the format that CKEditor decides on.