[Fix WICG#307] Define "Assigned Slot"

spec/shadow/index.html

@@ -280,6 +280,10 @@ <h3>Slots</h3>
           A <dfn>slot</dfn> is a defined location where nodes in a different <a>node tree</a> appear instead of the nodes's original position when constructing a <a>composed tree</a>.
         </p>
 
+        <p>
+          A node can be <dfn>assigned</dfn> to a slot, called an <dfn>assigned slot</dfn>. The exact algorithm of determining an <a>assigned slot</a> for a node is specified later.
+        </p>
+
         <p>A <dfn>distribution</dfn> is the mechanism that determines which <a data-lt="node">nodes</a> appear at each <a>slot</a>. The exact algorithm of a <a>distribution</a> is specified later.</p>
 
         <figure>
@@ -309,7 +313,7 @@ <h3>Slots</h3>
         <h2>Slotting Algorithm</h2>
 
         <p>
-          The <dfn>slotting algorithm</dfn> <strong>must</strong> be used to determine an assigned slot for a node and <strong>must</strong> be <a data-lt="processing equivalence">equivalent</a> to processing the following steps:
+          The <dfn>slotting algorithm</dfn> <strong>must</strong> be used to determine an <a>assigned slot</a> for a node and <strong>must</strong> be <a data-lt="processing equivalence">equivalent</a> to processing the following steps:
         </p>
 
         <div class="algorithm">