[css-text-3] Hanging/collapsing of fixed-width spaces

Closes w3c#3879

Author: frivoal

css-text-3/Overview.bs

@@ -1049,7 +1049,8 @@ Text Processing</h3>
   <h3 id="white-space-rules">
     The White Space Processing Rules</h3>
 
-    <p>White space processing in CSS affects only
+    <p>Except where specified otherwise,
+    White space processing in CSS affects only
       the <dfn export lt="white space|white space characters| document white space|document white space characters">document white space characters</dfn>:
       spaces (U+0020), tabs (U+0009), and <a href="#white-space-processing">segment breaks</a>.
 
@@ -1076,6 +1077,17 @@ Text Processing</h3>
       However, since both include spaces (U+0020), tabs (U+0009), and line feeds (U+000A)
       most authors won't notice any differences.
 
+    <p>Besides
+      Space (U+0020)
+      and No-Break Space (U+00A0),
+      Unicode [[UNICODE]] defines a number of additional space separator characters.
+      In this specification
+      all characters in the Unicode Zs category (See [[!UAX44]])
+      except Space (U+0020)
+      and No-Break Space (U+00A0)
+      are collectively referred to as
+      <dfn>other space separators</dfn>.
+
     <h4 id="white-space-phase-1">Phase I: Collapsing and Transformation</h4>
 
     <p>For each inline (including anonymous inlines;
@@ -1508,7 +1520,7 @@ Text Processing</h3>
       <li>A sequence at the end of a line
         (ignoring any intervening <a>inline box</a> boundaries)
         of <a>collapsible</a> spaces (U+0020)
-        and/or ideographic spaces (U+3000) whose 'white-space' value collapses spaces
+        and/or [=other space separators=] whose 'white-space' value collapses spaces
         is removed.
 
         <wpt>
@@ -1531,7 +1543,7 @@ Text Processing</h3>
           white-space-processing-047.xht
         </wpt>
       <li>If there remains any sequence of <a>white space</a>
-        and/or ideographic spaces (U+3000)
+        and/or [=other space separators=]
         at the end of a line:
         <ul>
           <li>If 'white-space' is set to ''pre-wrap'',
@@ -2179,7 +2191,7 @@ Line Breaking Details</h3>
       <code>NU</code>, <code>AL</code>, <code>AI</code>, or <code>ID</code>
       Unicode line breaking classes [[!UAX14]]).
       It does not affect rules governing the <a>soft wrap opportunities</a>
-      created by spaces (including U+3000 IDEOGRAPHIC SPACE) and around punctuation.
+      created by spaces (including [=other space separators=]) and around punctuation.
       (See 'line-break' for controls affecting punctuation and small kana.)
 
       <wpt>