this returns a nodeList, and nodeLists are live views on the iframe's document. It is possible for the browser to change the iframe's content while you're working with this nodeList, so if we're going to use this for iterating over "later" (which this code does), then either grab it just before you start iterating over the content, or grab it and immediately convert it to an array (using "nodeList = Array.prototype.slice.apply(iframeDocument.querySelectorAll('meta'));") so that its content remains stable throughout the function.