fix: dir's auto definition (#1118)

index.html

@@ -487,7 +487,20 @@ <h3>
  "<dfn data-dfn-for="text-direction">auto</dfn>" (default)
  </dt>
  <dd>
- No explicit directionality.
+ <p>
+ Direction determined from content using <a data-cite=
+ "bidi#P2">Rule P2</a> of the [[BIDI]] algorithm.
+ </p>
+ <aside class="note">
+ <p>
+ [=text-direction/auto=] means that the directionality of each
+ member is determined by its first strongly directional
+ character (as per the <a data-cite="bidi#P2">Rule P2</a>). An
+ explicit direction value such as "[=text-direction/rtl=]" or
+ "[=text-direction/ltr=]" is preferred to relying on the default
+ of "[=text-direction/auto=]".
+ </p>
+ </aside>
  </dd>
  </dl>
  <p>