/usr/share/zsh/5.5.1/functions
Edit: /usr/share/zsh/5.5.1/functions/_newsgroups (210B)
#autoload
local expl
: ${(A)_cache_newsgroups:=${${(f)"$(fgrep -vh \! ~/.newsrc*)"}%:*}}
(( ${(w)#_cache_newsgroups} )) && _wanted newsgroups expl 'newsgroup' \
_multi_parts "$@" -i . _cache_newsgroups