[css-text-4] Guidance for UA activation and related authoring practices

Author: frivoal

css-text-4/Overview.bs

@@ -251,6 +251,28 @@ Detecting Word Boundaries: the 'word-boundary-detection' property</h4>
 		</code></pre>
 	</div>
 
+	User Agents may activate
+	language-specific content analysis
+	in response to user preferences.
+	User Agents with this behavior must do this
+	by setting the [=declared value=] of 'word-boundary-detection' to ''word-boundary-detection/auto(<<lang>>)''
+	in the [=User Origin=].
+	User Agents that do not support the [=User Origin=]
+	may use the [=User Agent Origin=] instead.
+
+	<div class=advisement>
+		Manual analysis of the content can be more reliable than UA heuristics.
+		For best results, authors who can perform this analysis are encouraged to markup their documents
+		using <{wbr}> or U+200B
+		to exhaustively indicate word boundaries.
+
+		Authors who prepare their content in this manner
+		should not rely on the initial value, and
+		should explicitely specify ''word-boundary-detection: manual'' on the relevant parts of the content,
+		in order to override a potential ''word-boundary-detection: auto(<<lang>>)''
+		in the [=User Origin=] or [=User Agent Origin=].
+	</div>
+
 	[=Virtual word boundary=] insertion happens before [[CSS-TEXT-3#white-space-phase-1]]
 	and before [[#word-boundary-expansion]].
 	Later operations