deferred-for-level-5

<h3 id="idref-combinators">
Reference combinators <code>/ref/</code></h3>

	The <dfn export>reference combinator</dfn> consists of two slashes
	with an intervening <a href="http://www.w3.org/TR/css3-namespace/#css-qnames">CSS qualified name</a>,
	and separates two <a>compound selectors</a>,
	e.g. ''A /attr/ B''.
	The element represented by the first <a>compound selector</a>
	explicitly references
	the element represented by the second <a>compound selector</a>.
	Unless the host language defines a different syntax for expressing this relationship,
	this relationship is considered to exist if
	the value of the specified attribute on the first element is an IDREF or an <a>ID selector</a>
	referencing the second element.

	Attribute matching for reference combinators follow the same rules as for <a href="http://www.w3.org/TR/css3-selectors/#attribute-selectors">attribute selectors</a>.

	<div class="example">
		The following example highlights an <a element>input</a> element
		when its <a href="http://www.w3.org/TR/html40/interact/forms.html#h-17.9"><code>&lt;label></code></a>
		is focused or hovered-over:

		<pre>
		label:matches(:hover, :focus) /for/ input,       /* association by "for" attribute */
		label:matches(:hover, :focus):not([for]) input { /* association by containment */
			box-shadow: yellow 0 0 10px;
		}
		</pre>
	</div>