Currently, [locale.time.put.members] contains a footnote saying that "Although the C programming language defines no modifiers, most vendors do.", which is present since C++98. However, this should be no longer true since C99 (referenced by C++11/14) via WG14 N715.

It seems that we should delete the footnote, and explicitly mention the E and O specifiers specified in C together with implementation-defined extensions here. Not sure whether LWG issue is desired.