Add info on note title class changes for #29

dev_ref/migrating-to-2.2.dita

@@ -19,6 +19,13 @@
           <option>XHTML</option> plugin has been moved to a separate <option>HTML5</option> plugin.
         Customizations that extended the previous HTML5 output under the <option>XHTML</option>
         plugin will probably need to be refactored on the new HTML5 plugin.</p>
+      <p>Note title processing has been revised to use a common <codeph>note__title</codeph> class for note elements of
+        all types. The legacy <codeph><varname>{$type}</varname>title</codeph> classes (such as
+          <codeph>.notetitle</codeph>, <codeph>.cautiontitle</codeph>, <codeph>.tiptitle</codeph>, etc.) are included
+        for backwards compatibility, but are deprecated and will be removed in an upcoming release. Stylesheets that
+        apply formatting overrides to note titles should be revised to replace the deprecated class selectors with the
+        equivalent descendant selectors, for example <codeph>.note_note .note__title</codeph>, <codeph>.note_caution
+          .note__title</codeph>, <codeph>.note_tip .note__title</codeph>, etc.</p>
     </section>
     <section>
       <title>PDF</title>