The srcdoc iframe below should use this document's URL as its referrer. 

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Frame: '<!--frame1-->'
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This iframe logs information about its referrer:


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Frame: '<!--frame2-->'
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HTTP Referer header is http://127.0.0.1:8000/security/srcdoc-inherits-referrer.html
Referrer is http://127.0.0.1:8000/security/srcdoc-inherits-referrer.html