As a web developer, I have to support several different browsers at different versions. But recently, I had a discussion with a manager and the client wanted us to continue supporting ie11. I don't think the site should, but it does raise an interesting question. How far back in versions do you other web devs and designers support?
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If your site is already active, I would also look at Google Analytics and see if any of your audience uses IE11.
And the last question, the user experience will, of course, be best on evergreen browsers, but will it completely break on older browsers?