[css-fonts-4] More privacy considerations, more nuance, #5421

Author: svgeesus

css-fonts-4/Overview.bs

@@ -7463,6 +7463,8 @@ Installed Fonts</h3>
 
 A font may be installed globally on a device. Such fonts are generally accessible in any application, even applications which have no concept of CSS. The file or files backing the font object exist on the user's device, not as a remote resource.
 
+The set of <a href="#installed-fonts">installed fonts</a> available in the <a href="#font-matching-algorithm">Font Matching Algorithm</a> is explicitly undefined.
+
 Installed Fonts must not be Web Fonts, and Web Fonts must not be Installed Fonts.
 
 <h3 id="web-fonts">
@@ -7481,7 +7483,15 @@ Web Fonts shadow Installed Fonts, so if an Installed Font has the same family na
 <h3 id="preinstalled-and-user-installed-fonts">
 Preinstalled Fonts and User-Installed Fonts</h3>
 
-Users may choose to install fonts on their devices. User-Installed Fonts are installed by an explicit action by the user, such as clicking an "Install" button or copying a file into a particular directory on their device. Such fonts are User-Installed Fonts and also are Installed Fonts. Web content authors should not expect the presence of user-installed fonts, because there is no guarantee any user will have performed the action to install a specific font. User agents may choose to ignore User-Installed Fonts for the purpose of the <a href="#font-matching-algorithm">Font Matching Algorithm</a>.
+Users can choose to install fonts on their devices. 
+User-Installed Fonts are installed by an explicit action by the user, 
+such as clicking an "Install" button 
+or copying a file into a particular directory on their device. 
+Such fonts are User-Installed Fonts and also are Installed Fonts. 
+Web content authors should not count on the presence of user-installed fonts, 
+because there is no guarantee any user will have 
+performed the action to install a specific font. 
+User agents may choose to ignore User-Installed Fonts for the purpose of the <a href="#font-matching-algorithm">Font Matching Algorithm</a>.
 
 Any Installed Font which is not a User-Installed font is a Preinstalled Font. It is likely that all users of a particular version of a particular Operating System will have the same set of Preinstalled Fonts installed. As such, Web content authors targeting these Operating Systems may wish to use these fonts' family names inside 'font-family!!property' properties.
 
@@ -7989,6 +7999,23 @@ or because the latency or download time would make it's use infeasible,
 particularly for languages with a large character repertoire,
 or on slow or metered connections.
 
+Note: The set of <a href="#installed-fonts">installed fonts</a> 
+available in the <a href="#font-matching-algorithm">Font Matching Algorithm</a> 
+is explicitly undefined. 
+The available set of fonts <a href="https://panopticlick.eff.org">is</a> 
+used by trackers to fingerprint users and reduce their privacy. 
+However, some <a href="#installed-fonts">installed fonts</a>, 
+even some <a href="#preinstalled-and-user-installed-fonts">user-installed fonts</a>, 
+are required to make languages readable. 
+User Agents may choose to make all installed fonts available 
+for language support and design integrity reasons, 
+or may choose to make some fonts unavailable for privacy reasons. 
+In addition, User Agents may have additional facilities for fine-tuning this balance, 
+such as interfaces to allow users to explicitly make 
+certain fonts available or unavailable. 
+Different User Agents, even running on the same Operating System, 
+are expected to strike different balances here.
+
 In the case of user agents which perform rendering of local resources
 (such as an HTML and CSS to PDF renderer,
 or a Web-based wordprocessor)