*** DO NOT LAND *** Attempt to understand Regions complexity

Source/core/css/StyleInvalidationAnalysis.cpp

 /*
  * Copyright (C) 2012 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 105 matching lines @@
     case StyleRule::Import: // Whatever we import should do its own analysis, we don't need to invalidate the document here!
     case StyleRule::Keyframes: // Keyframes never cause style invalidations and are handled during sheet insertion.
     case StyleRule::Page: // Page rules apply only during printing, we force a full-recalc before printing.
         return false;
 
     case StyleRule::Media: // If the media rule doesn't apply, we could avoid recalc.
     case StyleRule::FontFace: // If the fonts aren't in use, we could avoid recalc.
     case StyleRule::Supports: // If we evaluated the supports-clause we could avoid recalc.
     case StyleRule::Viewport: // If the viewport doesn't match, we could avoid recalcing.
     // FIXME: Unclear if any of the rest need to cause style recalc:
-    case StyleRule::Region:
     case StyleRule::Filter:
         return true;
 
     // These should all be impossible to reach:
     case StyleRule::Unknown:
     case StyleRule::Charset:
     case StyleRule::Keyframe:
     case StyleRule::Style:
         break;
     }
@@ skipping 72 matching lines @@
             element->setNeedsStyleRecalc();
             // The whole subtree is now invalidated, we can skip to the next sibling.
             element = ElementTraversal::nextSkippingChildren(*element);
             continue;
         }
         element = ElementTraversal::next(*element);
     }
 }
 
 }