Proposed resolution:

This wording is relative to N4830.

1. Modify [range.access.begin] as follows:

   -1- The name ranges::begin denotes a customization point object ([customization.point.object]). The expression ranges::begin(E) for some subexpression E is expression-equivalent to:

   (1.1) — E + 0 if E is an lvalue of array type ([basic.compound]).

   (1.2) — Otherwise, if E is an lvalue, decay-copy(E.begin()) if it is a valid expression and its type I models input_or_output_iterator.

   (1.3) — Otherwise, decay-copy(begin(E)) if it is a valid expression and its type I models input_or_output_iterator with overload resolution performed in a context that includes the declarations:

   template<class T> void begin(T&&) = delete;
   template<class T> void begin(initializer_list<T>&&) = delete;
   

   and does not include a declaration of ranges::begin.

   […]

2. Modify [range.access.end] as follows:

   -1- The name ranges::end denotes a customization point object ([customization.point.object]). The expression ranges::end(E) for some subexpression E is expression-equivalent to:

   (1.1) — E + extent_v<T> if E is an lvalue of array type ([basic.compound]) T.

   (1.2) — Otherwise, if E is an lvalue, decay-copy(E.end()) if it is a valid expression and its type S models sentinel_for<decltype(ranges::begin(E))>

   (1.3) — Otherwise, decay-copy(end(E)) if it is a valid expression and its type S models sentinel_for<decltype(ranges::begin(E))> with overload resolution performed in a context that includes the declarations:

   template<class T> void end(T&&) = delete;
   template<class T> void end(initializer_list<T>&&) = delete;
   

   and does not include a declaration of ranges::end.

   […]

3. Modify [range.access.rbegin] as follows:

   -1- The name ranges::rbegin denotes a customization point object ([customization.point.object]). The expression ranges::rbegin(E) for some subexpression E is expression-equivalent to:

   (1.1) — If E is an lvalue, decay-copy(E.rbegin()) if it is a valid expression and its type I models input_or_output_iterator.

   (1.2) — Otherwise, decay-copy(rbegin(E)) if it is a valid expression and its type I models input_or_output_iterator with overload resolution performed in a context that includes the declarations:

   template<class T> void rbegin(T&&) = delete;
   template<class T> void rbegin(initializer_list<T>) = delete;
   

   and does not include a declaration of ranges::rbegin.

   […]

4. Modify [range.access.rend] as follows:

   -1- The name ranges::rend denotes a customization point object ([customization.point.object]). The expression ranges::rend(E) for some subexpression E is expression-equivalent to:

   (1.1) — If E is an lvalue, decay-copy(E.rend()) if it is a valid expression and its type S models

   sentinel_for<decltype(ranges::rbegin(E))>
   

   (1.2) — Otherwise, decay-copy(rend(E)) if it is a valid expression and its type S models

   sentinel_for<decltype(ranges::rbegin(E))>
   

   with overload resolution performed in a context that includes the declarations:

   template<class T> void rend(T&&) = delete;
   template<class T> void rend(initializer_list<T>) = delete;
   

   and does not include a declaration of ranges::rend.

   […]

[ 2021-06-23 Resolved by adoption of P2091R0 in Prague. Status changed: New → Resolved. ]

[ 2019-10 Priority set to 3 after reflector discussion ]

The specification of ranges::begin in [range.access.begin] includes a "poison pill" overload:

template<class T> void begin(initializer_list<T>&&) = delete;

ranges::end ([range.access.end]) has a similar poison pill for initializer_list, which should be changed consistently.

Notably ranges::rbegin ([range.access.rbegin]) and ranges::rend ([range.access.rbegin]) as currently specified accept rvalue initializer_list arguments; they find the initializer_list overloads of std::rbegin and std::rend ([iterator.range]) via ADL. While I can't put my finger on anything in particular that's broken by this behavior, it seems wise to make rbegin and rend consistent with begin and end for initializer_list until and unless we discover a reason to do otherwise.