title: How to check if the selected text is editable?
body: <p>I'm working on a Chrome extension that deals with text selection. I want to detect whether the selected text is editable. Given a <a href="https://developer.mozilla.org/en-US/docs/Web/API/Selection" rel="nofollow">Selection</a> object returned by <a href="https://developer.mozilla.org/en-US/docs/Web/API/Window.getSelection" rel="nofollow">getSelection()</a>, is it possible to check whether the selected text is editable? How?</p>