JavaScript, cookie syncing and the Same Origin Policy

Hi,

I understand that advertising cookies collude with one another to exchange different identifiers used for the same browser/user in a process referred to as cookie syncing. I've read a number of different descriptions of how this happens, such as the use of redirects. But there's something very basic that I don't get about all this: why is this not prevented by Same Origin Policy? What is different about the way cookie-handling is handled by client-side scripts, in comparison with …

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