<style>
    ::part(woot) {
      background: green;
    }
  </style>

Given this style at level n of a composed tree of ShadowDOM tree, this element should match if it's at level n+m of the composed tree where m is 0 or more.

<div part="woot">w00t!</div>

This would let developers use part to target elements through ShadowDOM without having to worry about whether or not elements are nested inside additional shadowRoots or even if they are in ShadowDOM at all.

These would all match at the document level or inside a shadowRoot:

<style> ::part(woot)</style>
<div part="woot">match, w00t!</div>
<div>
SR
  <div>
  SR
    <div part="woot">match, w00t!</div>