[functional.syn, func.bind.isplace] Improve how we talk about placeholder placeholders as opposed to concrete placeholders

Author: tkoeppe

source/utilities.tex

@@ -12712,7 +12712,8 @@
 \begin{codeblock}
 namespace std {
   // \ref{func.invoke}, invoke
-  template <class F, class... Args> result_of_t<F&&(Args&&...)> invoke(F&& f, Args&&... args);
+  template <class F, class... Args>
+    result_of_t<F&&(Args&&...)> invoke(F&& f, Args&&... args);
 
   // \ref{refwrap}, reference_wrapper
   template <class T> class reference_wrapper;
@@ -12772,7 +12773,8 @@
   template <> struct bit_not<void>;
 
   // \ref{func.not_fn}, function template \tcode{not_fn}
-  template <class F> @\unspec@ not_fn(F&& f);
+  template <class F>
+    @\unspec@ not_fn(F&& f);
 
   // \ref{func.bind}, bind
   template<class T> struct is_bind_expression;
@@ -12784,17 +12786,18 @@
     @\unspec@ bind(F&&, BoundArgs&&...);
 
   namespace placeholders {
-    // M is the \impldef{number of placeholders for bind expressions} number of placeholders
-    @\seebelow@ _1;
-    @\seebelow@ _2;
-                .
-                .
-                .
-    @\seebelow@ _M;
+    // \tcode{\placeholder{M}} is the \impldef{number of placeholders for bind expressions} number of placeholders
+    @\seebelownc@ _1;
+    @\seebelownc@ _2;
+               .
+               .
+               .
+    @\seebelownc@ _@\placeholdernc{M}@;
   }
 
   // \ref{func.memfn}, member function adaptors
-  template<class R, class T> @\unspec@ mem_fn(R T::*) noexcept;
+  template<class R, class T>
+    @\unspec@ mem_fn(R T::*) noexcept;
 
   // \ref{func.wrap}, polymorphic function wrappers
   class bad_function_call;
@@ -14069,12 +14072,12 @@
 Instantiations of the \tcode{is_placeholder} template shall meet
 the \tcode{UnaryTypeTrait} requirements~(\ref{meta.rqmts}). The implementation
 shall provide a definition that has the base characteristic of
-\tcode{integral_constant<int, J>} if \tcode{T} is the type of
-\tcode{std::placeholders::_J}, otherwise it shall have a
+\tcode{integral_constant<int, \placeholder{J}>} if \tcode{T} is the type of
+\tcode{std::placeholders::_\placeholder{J}}, otherwise it shall have a
 base characteristic of \tcode{integral_constant<int, 0>}. A program
 may specialize this template for a user-defined type \tcode{T} to
-have a base characteristic of \tcode{integral_constant<int, \textit{N}>}
-with \tcode{\textit{N} > 0} to indicate that \tcode{T} should be
+have a base characteristic of \tcode{integral_constant<int, N>}
+with \tcode{N > 0} to indicate that \tcode{T} should be
 treated as a placeholder type.
 
 \rSec3[func.bind.bind]{Function template \tcode{bind}}