This is very nicely done, however css viewport units have what appears to be the same browser support and are built-in. I think what this delivers that css doesn't is explicit bounds for min and max size, whereas you'd have to do a media query or something to set those in a pure css solution.

This is nice because it's completely flexible/dynamic. You don't have to worry about declaring font sizes for every screen width or breakpoint. That would require an unnecessary amount of media queries...

Well viewport units are completely flexible/dynamic [1]. That's their purpose. But I can see how this library might be a quicker solution in many cases.

[1] http://dev.w3.org/csswg/css-values/#viewport-relative-length...

Very true. Unfortunately, the support for viewport units is somewhat lacking. Some browsers still require javascript to "repaint" the elements after a manual window resize. It's only a matter of time though, when these JS patches won't be necessary...can't wait.