[css-fonts-4] Mention in-extremis privacy options w3c#5578

Author: svgeesus

css-fonts-4/Overview.bs

@@ -6443,6 +6443,14 @@ whether the font was loaded.
 This takes time, and checking for more than a few hundred fonts
 introduces a noticeable delay in page rendering.
 
+For <em>especially privacy-sensitive contexts</em>,
+options would include never downloading any webfonts
+(at the risk that some characters may be rendered incorrectly, or not at all),
+or always downloading all webfonts whether needed or not
+(ignoring unicode-range,
+and potentially downloading vast quantities of unused fonts
+each time the page is viewed).
+
 <h3 id="sp202">Is this specification exposing the minimum amount of information necessary to power the feature? </h3>
 
 An emerging consensus is that a User Agent must expose Preinstalled Fonts