[const.iterators] Add subclause structure.

Author: tkoeppe

source/iterators.tex

@@ -335,11 +335,17 @@
       inserter(Container& x, ranges::iterator_t<Container> i);                      // freestanding
 
   // \ref{const.iterators}, constant iterators and sentinels
+  // \ref{const.iterators.alias}, alias templates
   template<@\libconcept{indirectly_readable}@ I>
     using iter_const_reference_t = @\seebelow@;                                       // freestanding
   template<class Iterator>
     concept @\exposconcept{constant-iterator}@ = @\seebelow@; // \expos
+  template<@\libconcept{input_iterator}@ I>
+    using const_iterator = @\seebelow@;                                               // freestanding
+  template<class S>
+    using const_sentinel = @\seebelow@;                                               // freestanding
 
+  // \ref{const.iterators.iterator}, class template \tcode{basic_const_iterator}
   template<class Iterator>
     class basic_const_iterator;                                                     // freestanding
 
@@ -356,12 +362,6 @@
     using type = basic_const_iterator<common_type_t<T, U>>;
   };
 
-  template<@\libconcept{input_iterator}@ I>
-    using const_iterator = @\seebelow@;                                               // freestanding
-
-  template<class S>
-    using const_sentinel = @\seebelow@;                                               // freestanding
-
   template<@\libconcept{input_iterator}@ I>
     constexpr const_iterator<I> make_const_iterator(I it) { return it; }            // freestanding
 
@@ -4157,6 +4157,8 @@
 
 \rSec2[const.iterators]{Constant iterators and sentinels}
 
+\rSec3[const.iterators.general]{General}
+
 \pnum
 Class template \tcode{basic_const_iterator} is an iterator adaptor
 with the same behavior as the underlying iterator
@@ -4169,6 +4171,8 @@
 \pnum
 Specializations of \tcode{basic_const_iterator} are constant iterators.
 
+\rSec3[const.iterators.alias]{Alias templates}
+
 \begin{itemdecl}
 template<@\libconcept{indirectly_readable}@ It>
   using iter_const_reference_t = common_reference_t<const iter_value_t<It>&&,
@@ -4201,11 +4205,13 @@
 Otherwise, \tcode{S}.
 \end{itemdescr}
 
-\begin{codeblock}
-template<class I>
-  concept @\exposconcept{not-a-const-iterator}@ = @\seebelow@;
+\rSec3[const.iterators.iterator]{Class template \tcode{basic_const_iterator}}
 
+\begin{codeblock}
 namespace std {
+  template<class I>
+    concept @\exposconcept{not-a-const-iterator}@ = @\seebelow@;
+
   template<@\libconcept{input_iterator}@ Iterator>
   class @\libglobal{basic_const_iterator}@ {
     Iterator @\exposid{current_}@ = Iterator();
@@ -4318,6 +4324,8 @@
 if \tcode{I} is a specialization of \tcode{basic_const_iterator} and
 \tcode{true} otherwise.
 
+\rSec3[const.iterators.types]{Member types}
+
 \pnum
 \tcode{basic_const_iterator<Iterator>::iterator_concept} is defined as follows:
 \begin{itemize}
@@ -4344,6 +4352,8 @@
 \tcode{basic_const_iterator<Iterator>::iterator_category} denotes
 the type \tcode{iterator_traits<\brk{}Iterator>::iterator_category}.
 
+\rSec3[const.iterators.ops]{Operations}
+
 \indexlibraryctor{basic_const_iterator}%
 \begin{itemdecl}
 constexpr basic_const_iterator(Iterator current);