zsh/Completion/Core/_compalso

#autoload

# This searches $* in the array for normal completions and calls the result.
# It is used to include completions for another command or special context
# into the list generated by the calling function.
# For example the function for `-subscript-' could call this as in
# `_compalso -math-' to get the completions that would be generated for a
# mathematical context.

local i tmp ret=1

for i; do
  tmp="$_comps[$1]"
  [[ -z "$tmp" ]] || "$tmp" && ret=0
done

return ret