title: Why is a transition property on the placeholder pseudoelement valid in Chrome?
body: <p>I was goofing around with the <code>::placeholder</code> pseudoelement on Codepen (Chrome 59.0.3071) when I noticed something odd. (please see my <a href="https://jsfiddle.net/4ct6zkaw/" rel="noreferrer">JSFiddle</a>)</p>
  
  <p>In brief, this CSS should not enable a transition of the <code>::placeholder</code> color over 2s:</p>
  
  <pre><code>input::placeholder {color:red;transition:2s;}
  input:hover::placeholder {color:green}
  </code></pre>
  
  <p>Using Firefox, there is no color transition over a 2 second interval on hover  (this appears to be correct according to <a href="https://drafts.csswg.org/css-transitions/#propdef-transition" rel="noreferrer">this section</a> of a W3C spec and <a href="https://drafts.csswg.org/css-pseudo-4/#placeholder-pseudo" rel="noreferrer">this section</a> of a different one - follow the thread to the <code>::first-line</code> pseudo-element), but instead there is an immediate color transition to green;</p>
  
  <p>However, the same JSFiddle using Chrome <em>does</em> show a <code>::placeholder</code> color transition over a period of 2 seconds, which according to the specs, appears to be incorrect.</p>
  
  <p><em>Is this a bug in this version of Chrome (and if so, is it being addressed?) or is this an indictment of my lack of understanding of CSS?</em></p>