On Wednesday, November 4, 2020 6:21 PM, D'Alessandro, Luke K <ldalessa@iu.edu> wrote:

Do you have an example of somewhere else in the standard that defines such an “exposition-only type” that I could use for reference language? (I presume that this means that the actual type name is implementation-defined, though the definition must be equivalent to “struct zero_length_array_tag{};").

There is an exposition-only alias in [sequences.general].

Something like this:

The following exposition-only class may appear in the
definitions in this subclause:

  struct zero-length-array-tag {};

Zhihao Yuan, ID lichray
The best way to predict the future is to invent it.