Make fallback table more robust for aria-valuenow on slider role

index.html

@@ -12119,7 +12119,7 @@ <h3>States and Properties</h3>
 				<tr>
 					<td><rref>slider</rref></td>
 					<td><pref>aria-valuenow</pref></td>
-					<td><code>(aria-valuemax - aria-valuemin) / 2</code></td>
+					<td>If missing or not a <a href="#valuetype_number">number</a>,<code>(aria-valuemax - aria-valuemin) / 2</code>. If present but less than <code>aria-valuemin</code>, the value of <code>aria-valuemin</code>. If present but greater than <code>aria-valuemax</code>, the value of <code>aria-valuemax</code>. </td>
 				</tr>
 				<tr>
 					<td><rref>spinbutton</rref></td>