This securityrestriction is to avoid cross-site scripting attacks (XSS).
这个安全限制是为了避免跨站点脚本攻击(XSS)。
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The SOP is a securityrestriction that basically forbids a page loaded from a certain origin (meaning the protocol/host/port trio of the URL) to access data from a different origin.
This should only work if the client and the server are on the same machine, and no special restriction logic is implemented in the customized security plug-ins.