* doc/emacs/help.texi (Help Mode): Document it (bug#36767). * lisp/help-fns.el (help-fns-function-description-header) (describe-variable, describe-face, describe-keymap) (describe-mode): Add the required data. * lisp/help-mode.el (help-mode-map): Add 'i' and 's'. (help-mode--current-data): New variable. (help-mode): Make it local. (help-view-source, help-goto-info): New commands.