[css-font-loading] Rephrase one of the 'pending on env' conditions to be clearer that layout operations depending on recently-loaded fonts need to complete.

Author: tabatkins

css-font-loading/Overview.bs

@@ -574,7 +574,14 @@ The <code>FontFaceSet</code> Interface</h2>
 
 	* the document is still loading
 	* the document has pending stylesheet requests
-	* the document has pending layout operations which might cause the user agent to request a font.
+	* the document has pending layout operations which might cause the user agent to request a font,
+		or which depend on recently-loaded fonts
+
+	Note: The idea is that once a {{FontFaceSet}} stops being <a>pending on the environment</a>,
+	as long as nothing further changes the document,
+	an author can depend on sizes/positions of things being "correct" when measured.
+	If the above conditions do not fully capture this guarantee,
+	they need to be amended to do so.
 
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