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

Source/core/rendering/RenderGrid.cpp

 /*
  * Copyright (C) 2011 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 241 matching lines @@
 {
     ASSERT(needsLayout());
 
     if (!relayoutChildren && simplifiedLayout())
         return;
 
     // FIXME: Much of this method is boiler plate that matches RenderBox::layoutBlock and Render*FlexibleBox::layoutBlock.
     // It would be nice to refactor some of the duplicate code.
     LayoutRepainter repainter(*this, checkForRepaintDuringLayout());
     LayoutStateMaintainer statePusher(view(), this, locationOffset(), hasTransform() || hasReflection() || style()->isFlippedBlocksWritingMode());
-
-    // Regions changing widths can force us to relayout our children.
-    RenderFlowThread* flowThread = flowThreadContainingBlock();
-    if (logicalWidthChangedInRegions(flowThread))
-        relayoutChildren = true;
-    if (updateRegionsAndShapesLogicalSize(flowThread))
-        relayoutChildren = true;
-
     LayoutSize previousSize = size();
 
     setLogicalHeight(0);
     updateLogicalWidth();
 
     layoutGridItems();
 
     LayoutUnit oldClientAfterEdge = clientLogicalBottom();
     updateLogicalHeight();
 
     if (size() != previousSize)
         relayoutChildren = true;
 
     layoutPositionedObjects(relayoutChildren || isRoot());
 
-    computeRegionRangeForBlock(flowThread);
-
     computeOverflow(oldClientAfterEdge);
     statePusher.pop();
 
     updateLayerTransform();
 
     // Update our scroll information if we're overflow:auto/scroll/hidden now that we know if
     // we overflow or not.
     if (hasOverflowClip())
         layer()->scrollableArea()->updateAfterLayout();
 
@@ skipping 856 matching lines @@
     if (isOutOfFlowPositioned())
         return "RenderGrid (positioned)";
     if (isAnonymous())
         return "RenderGrid (generated)";
     if (isRelPositioned())
         return "RenderGrid (relative positioned)";
     return "RenderGrid";
 }
 
 } // namespace WebCore