[css-break-3] Clarify the case where the UA may treat inline-level boxes as fragmentable or monolithic. w3c#1111

Author: fantasai

css-break-3/Overview.bs

@@ -575,7 +575,12 @@ Possible Break Points</h3>
     Since line boxes contain no possible break points,
     ''inline-block'' and ''inline-table'' boxes
     (and other inline-level <a>display types</a> that establish an <a>independent formatting context</a>)
-    may also be considered <a>monolithic</a>.
+    may also be considered <a>monolithic</a>:
+    that is,
+    in the cases where a single line box is too large
+    to fit within its fragmentainer even by itself
+    and the UA chooses to split the line box,
+    it may fragment such boxes or it may treat them as monolithic.
 
 <h3 id="break-types">
 Types of Breaks</h3>