Tries various vendor prefixes and returns the first supported property.
function vendor(el, prop) {
    var s = el.style
      , pp
      , i

    if(s[prop] !== undefined) return prop
    prop = prop.charAt(0).toUpperCase() + prop.slice(1)
    for(i=0; i<prefixes.length; i++) {
      pp = prefixes[i]+prop
      if(s[pp] !== undefined) return pp
    }
  }