complete description of the main changes

as discussed last week
https://www.w3.org/2025/10/16-rdf-star-minutes.html

Author: pchampin

spec/index.html

@@ -104,7 +104,12 @@
     as a <a>triple term</a>, in the <a>object</a> position of another <a>triple</a>.
     RDF 1.2 also introduces <a>directional language-tagged strings</a>,
     which contain a <a>base direction</a> component that allows the
-    initial text direction to be specified for presentation by a user agent.</p>
+    initial text direction to be specified for presentation by a user agent.
+    Finally, to ease the transition from RDF 1.1 to RDF 1.2,
+    this specification introduces a mechanism for
+    <a href="#section-version-announcement">explicitly conveying</a>
+    which version of RDF is used by a given piece of data.
+  </p>
 
   <p>This specification introduces key concepts and terminology for RDF 1.2, and subsequently discusses
     datatyping and the handling of <a>fragment identifiers</a> in IRIs within