[css-text-3] Add more mentions of “collapsible” for clarity. w3c#3513

Author: fantasai

css-text-3/Overview.bs

@@ -1025,8 +1025,9 @@ Text Processing</h3>
       white space characters are considered <dfn export lt="collapsible white space|collapsible">collapsible</dfn>
       and are processed by performing the following steps:</p>
       <ol>
-        <li>All spaces and tabs immediately preceding or following a segment
-          break are removed.
+        <li>Any sequence of collapsible spaces and tabs
+          immediately preceding or following a <a>segment break</a>
+          is removed.
 
           <wpt>
             white-space/seg-break-transformation-000.html
@@ -1040,10 +1041,10 @@ Text Processing</h3>
             white-space-processing-010.xht
           </wpt>
         </li>
-        <li><a>Segment breaks</a> are transformed for
+        <li>Collapsible <a>segment breaks</a> are transformed for
           rendering according to the <a href="#line-break-transform">segment break transformation rules</a>.
         </li>
-        <li>Every tab is converted to a space (U+0020).
+        <li>Every collapsible tab is converted to a collapsible space (U+0020).
 
           <wpt>
             white-space/white-space-collapse-000.html
@@ -1054,7 +1055,7 @@ Text Processing</h3>
             white-space-processing-021.xht
           </wpt>
         </li>
-        <li>Any space immediately following another collapsible space&mdash;even
+        <li>Any collapsible space immediately following another collapsible space&mdash;even
           one outside the boundary of the inline containing that space,
           provided both spaces are within the same inline formatting
           context&mdash;is collapsed to have zero advance width. (It is