gistfile1.js

// selectorSupported lovingly lifted from the mad italian genius, diego perini
// http://javascript.nwbox.com/CSSSupport/
function selectorSupported(selector){
  
  var support, link, sheet, doc = document,
      root = doc.documentElement,
      head = root.getElementsByTagName('head')[0],

      impl = doc.implementation || {
              hasFeature: function() {
                  return false;
              }
      },

  link = doc.createElement("style");
  link.type = 'text/css';

  (head || root).insertBefore(link, (head || root).firstChild);

  sheet = link.sheet || link.styleSheet;

  if (!(sheet && selector)) return false;

  support = impl.hasFeature('CSS2', '') ?
  
              function(selector) {
                  try {
                      sheet.insertRule(selector + '{ }', 0);
                      sheet.deleteRule(sheet.cssRules.length - 1);
                  } catch (e) {
                      return false;
                  }
                  return true;
                  
              } : function(selector) {
                
                  sheet.cssText = selector + ' { }';
                  return sheet.cssText.length !== 0 && !(/unknown/i).test(sheet.cssText) && sheet.cssText.indexOf(selector) === 0;
              };
   
  return support(selector);

};


Modernizr.addTest('targetselector',function(){
  return selectorSupported(':target');
})

I'm sure this works great - but I can implement... an example would be very useful...

can't**

Awesome function, thank you very much.
Also thanks to javier, I wanted to test exaclty what he found, :nth-child(n).

This doesn't work on IE9:

>> selectorSupported('div ~ div')
false
>> selectorSupported('div + div')
false