Proposed resolution:

This wording is relative to the FDIS.

1. Change [func.bind.isbind] to:

   namespace std {
     template<class T> struct is_bind_expression; // see below
       : integral_constant<bool, see below> { };
   }
   

   -1- is_bind_expression can be used to detect function objects generated by bind. bind uses is_bind_expression to detect subexpressions. Users may specialize this template to indicate that a type should be treated as a subexpression in a bind call.

   -2- If T is a type returned from bind, is_bind_expression<T> shall be publicly derived from integral_constant<bool, true>, otherwise from integral_constant<bool, false>Instantiations of the is_bind_expression template shall meet the UnaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition that has a BaseCharacteristic of true_type if T is a type returned from bind, otherwise it shall have a BaseCharacteristic of false_type. A program may specialize this template for a user-defined type T to have a BaseCharacteristic of true_type to indicate that T should be treated as a subexpression in a bind call..

   -3- is_placeholder can be used to detect the standard placeholders _1, _2, and so on. bind uses is_placeholder to detect placeholders. Users may specialize this template to indicate a placeholder type.

   -4- If T is the type of std::placeholders::_J, is_placeholder<T> shall be publicly derived from integral_constant<int, J>, otherwise from integral_constant<int, 0>.

2. Insert a new sub-clause immediately following sub-clause [func.bind.isbind], the suggested sub-clause tag is [func.bind.isplace]:

   20.8.9.1.? Class template is_placeholder [func.bind.isplace]

   namespace std {
     template<class T> struct is_placeholder; // see below
   }
   

   -?- is_placeholder can be used to detect the standard placeholders _1, _2, and so on. bind uses is_placeholder to detect placeholders.

   -?- Instantiations of the is_placeholder template shall meet the UnaryTypeTrait requirements ([meta.rqmts]). The implementation shall provide a definition that has a BaseCharacteristic of integral_constant<int, J> if T is the type of std::placeholders::_J, otherwise it shall have a BaseCharacteristic of integral_constant<int, 0>. A program may specialize this template for a user-defined type T to have a BaseCharacteristic of integral_constant<int, N> with N > 0 to indicate that T should be treated as a placeholder type.