My hobby recently has been making website scale better on phones, but I ran into a problem on several of them: The viewport meta tag assumes that a website either has a fixed width or that it scales to any possible width. I investigated several solutions and eventually settled on an (apparently) novel one: Check the screen size, and if it's too small, add a new meta tag with a fixed viewport. I also wrote a JavaScript polyfill that lets me just set a min-width in the viewport tag.
