[css-text-3] Organize into subsections

and remove the note about possible futures.

Author: fantasai

css-text-3/Overview.bs

@@ -541,20 +541,6 @@ Text Processing</h3>
           </wpt>
     </dl>
 
-    <p>For ''capitalize'', what constitutes a “word“ is UA-dependent;
-      [[!UAX29]] is suggested (but not required)
-      for determining such word boundaries.
-      Authors should not expect ''capitalize'' to follow
-      language-specific titlecasing conventions
-      (such as skipping articles in English).
-      Out-of-flow elements and inline element boundaries
-      must not introduce a 'text-transform' word boundary
-      and must be ignored when determining such word boundaries.
-
-      <wpt>
-        text-transform/text-transform-capitalize-033.html
-      </wpt>
-
     <div class="example">
       <p>The following example converts the ASCII characters
         used in abbreviations in Japanese text to their fullwidth variants
@@ -609,9 +595,22 @@ Text Processing</h3>
       with all “s” characters substituted by “f”.
     </div>
 
-    <p class="note">
-      Note: As defined in <a href="#order">Text Processing Order of Operations</a>,
-      transforming text affects line-breaking and other formatting operations.
+<h4 id="text-transform-mapping">
+Mapping Rules</h4>
+
+    <p>For ''capitalize'', what constitutes a “word“ is UA-dependent;
+      [[!UAX29]] is suggested (but not required)
+      for determining such word boundaries.
+      Authors should not expect ''capitalize'' to follow
+      language-specific titlecasing conventions
+      (such as skipping articles in English).
+      Out-of-flow elements and inline element boundaries
+      must not introduce a 'text-transform' word boundary
+      and must be ignored when determining such word boundaries.
+
+      <wpt>
+        text-transform/text-transform-capitalize-033.html
+      </wpt>
 
     <p>
       The UA must use the full case mappings for Unicode
@@ -683,6 +682,9 @@ Text Processing</h3>
 
     <p>The mappings for small Kana to full-size Kana are defined in [[#small-kana]].
 
+<h4 id="text-transform-order">
+Order of Operations</h4>
+
     <p>When multiple values are specified and therefore multiple transformations need to be applied,
       they are applied in the following order:
     <ol>
@@ -708,10 +710,8 @@ Text Processing</h3>
       </wpt>
 
     <p class="note">
-      Note: A future level of CSS may introduce the ability to create custom mapping
-      tables for less common text transforms, such as by an ''@text-transform''
-      rule similar to ''@counter-style'' from [[CSS-COUNTER-STYLES-3]].
-
+      Note: As defined in <a href="#order">Text Processing Order of Operations</a>,
+      transforming text affects line-breaking and other formatting operations.
 
 <h2 id="white-space-property" oldids="white-space-collapsing,text-wrap">
   White Space and Wrapping: the 'white-space' property</h2>