这个polyfill如何为document.queryselectorall工作？

Question

我想了解queryselectorall的这个polyfill？ Specifially这一行：

styleTag.styleSheet.cssText = selector + "{x:expression(document.__qsaels.push(this))}"; 

https://gist.github.com/connrs/2724353

if (!document.querySelectorAll) { 
    document.querySelectorAll = function(selector) { 
     var doc = document, 
      head = doc.documentElement.firstChild, 
      styleTag = doc.createElement('STYLE'); 
     head.appendChild(styleTag); 
     doc.__qsaels = []; 

     styleTag.styleSheet.cssText = selector + "{x:expression(document.__qsaels.push(this))}"; 
     window.scrollBy(0, 0); 

     return doc.__qsaels; 
    } 
} 

Answer 1

据滥用CSS的expression "feature"。在计算x属性的风格（发生在由scrollBy(0, 0)触发的回流时）时，Internet Explorer将为与选择器匹配的所有元素执行此代码段。

CSS expressions are officially despised因为IE 8 ...