[css-text-3] Clarify relationship of space prioritization vs word-break/line-break.

Author: fantasai

css-text-3/Overview.bs

@@ -1886,15 +1886,28 @@ Line Breaking Details</h3>
         i18n/css3-text-line-break-baspglwj-130.html
         i18n/css3-text-line-break-baspglwj-131.html
       </wpt>
-    <li>UAs that allow wrapping at punctuation other than spaces should prioritize breakpoints.
+
+    <li>UAs that allow wrapping at punctuation
+      other than <a>word separators</a>
+      in writing systems that use them
+      <em>should</em> prioritize breakpoints.
       (For example, if breaks after slashes are given a lower priority than spaces,
-      the sequence "check /etc" will never break between the "/" and the "e".)
-      As long as care is taken to avoid such awkward breaks, allowing breaks at
-      appropriate punctuation other than spaces is recommended, as it results
-      in more even-looking margins, particularly in narrow measures.
+      the sequence “check /etc” will never break between the "/" and the "e".)
+      As long as care is taken to avoid such awkward breaks,
+      allowing breaks at appropriate punctuation other than <a>word separators</a>
+      is recommended,
+      as it results in more even-looking margins, particularly in narrow measures.
       The UA may use the width of the containing block, the text's language,
+      the 'line-break' value,
       and other factors in assigning priorities:
       CSS does not define prioritization of line breaking opportunities.
+      Prioritization of <a>word separators</a> is not expected,
+      however,
+      if ''word-break: break-all'' is specified
+      (since this value explicitly requests line breaking behavior
+      not based on breaking at <a>word separators</a>)--
+      and is forbidden under ''line-break: anywhere''.
+
     <li>Out-of-flow elements do not introduce a <a>forced line break</a>
       or <a>soft wrap opportunity</a> in the flow.