SVG foreignObject feature test
HTML
<svg width="100%" height="100%" version="1.1" xmlns="http://www.w3.org/2000/svg"
xmlns:xlink="http://www.w3.org/1999/xlink">
<foreignObject x="0" y="0" width="100%" height="100%">
<p>INCEPTIONfvgvqg!</p>
</foreignObject>
</svg>
JavaScript
if(document.implementation.hasFeature('http://www.w3.org/TR/SVG11/feature#Extensibility','1.1')){
alert('Your browser supports SVG foreignObject! As proof you should read a text named "INCEPTION!"');
}else {
alert('Poor you. Your browser does not support SVG foreignObject :(');
}