Create a go back button for an iframe from its owner document

I want 开发者_如何学Cto navigation in iframe history from it's owner document. I mean I have an iframe, and a button that is out of the iframe, in iframe's parent document. And I want to trigger go back for iframe with this button.

Any suggesstion?

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i would think that you would need to make a java script that sets a variable each time the iframe changes and then make a button to plug that variable in to the src