emacs-doc cannot be installed with emacs-x11 or -gtk
Since emacs-doc requires emacs-nox (which cannot be installed alongside
emacs-x11
or emacs-gtk), there is currently no way to install emacs-doc with the
emacs-x11 or
emacs-gtk2 packages.
(from redmine: issue id 8106, created on 2017-11-04)