LayoutTests/editing/selection/iframe-select.html - external/github.com/WebKit/webkit - Git at Google

 <!DOCTYPE html>
 <iframe id="iframe" style="width: 100px; height: 100px; will-change: transform; position: absolute; top: 50px; left: 50px" frameBorder=0 srcdoc="<div></div>"></iframe>
 <script>
     var selection = getSelection();

     selection.setBaseAndExtent(document.querySelector("#iframe"), 0, document.querySelector("#iframe"), 1);
 </script>
	<!DOCTYPE html>
	<iframe id="iframe" style="width: 100px; height: 100px; will-change: transform; position: absolute; top: 50px; left: 50px" frameBorder=0 srcdoc="<div></div>"></iframe>
	<script>
	var selection = getSelection();

	selection.setBaseAndExtent(document.querySelector("#iframe"), 0, document.querySelector("#iframe"), 1);
	</script>