[css-text-3] Explain about Suppress-Script

Author: fantasai

css-text-3/Overview.bs

@@ -5608,6 +5608,16 @@ Identifying the Content Writing System</h2>
 		</dl>
 	</div>
 
+	However, [[BCP47]] script subtags are not typically used
+	(and are in fact discouraged)
+	for languages strongly associated with a single writing system:
+	instead that writing system is expected to be implied
+	when no other is specified.
+	IANA maintains a database of various languages’ default writing systems
+	via the <code>Suppress-Script</code> field in its
+	<a href="https://www.iana.org/assignments/language-subtag-registry/language-subtag-registry">language subtag registry</a
+	for this purpose.
+
 	Note: More advice on language tagging can be found in
 	the <a href="https://www.w3.org/International/core/">Internationalization Working Group</a>’s
 	<a href="https://www.w3.org/International/articles/language-tags/">“Language tags in HTML and XML”</a>