Index: source
===================================================================
--- source	(revision 2856)
+++ source	(revision 2857)
@@ -25943,11 +25943,30 @@
   <code>th</code> element (as defined by the <span>table
   model</span>).</p>
 
+  <p>A <code>th</code> element with ID <var title="">id</var> is said
+  to be <i>directly targetted</i> by all <code>td</code> and
+  <code>th</code> elements in the same <span
+  title="concept-table">table</span> that have <code
+  title="attr-tdth-headers">headers</code> attributes whose values
+  include as one of their tokens the ID <var title="">id</var>. A
+  <code>th</code> element <var title="">A</var> is said to be
+  <i>targetted</i> by a <code>th</code> or <code>td</code> element
+  <var title="">B</var> if either <var title="">A</var> is <i>directly
+  targetted</i> by <var title="">B</var> or if there exists an element
+  <var title="">C</var> that is itself <i>targetted</i> by the element
+  <var title="">B</var> and <var title="">A</var> is <i>directly
+  targetted</i> by <var title="">C</var>.</p>
+
+  <p>A <code>th</code> element must not be <i>targetted</i> by
+  itself.</p>
+
   <p class="note">The <code title="attr-tdth-colspan">colspan</code>,
   <code title="attr-tdth-rowspan">rowspan</code>, and <code
   title="attr-tdth-headers">headers</code> attributes take part in the
   <span>table model</span>.</p>
 
+  <hr>
+
   <p>The <code>td</code> and <code>th</code> elements implement
   interfaces that inherit from the <code>HTMLTableCellElement</code>
   interface:</p>