After opening enriched.txt and running any kind of code using the
`font-lock-add-keywords` function (for example whitespace-mode or
hl-todo-mode), the enriched highlighting is gone.  Is this a bug or
intentional?  If it's intentional, is there some way for the code using
`font-lock-add-keywords` to detect this condition, other than checking
for the presence of enriched-mode?  Alternatively, is there a
recommended way to add highlighting of keywords that's compatible with
enriched-mode?


In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.20)
 of 2020-05-19 built on felixonmars2
Windowing system distributor 'The X.Org Foundation', version 11.0.12008000
System Description:	Arch Linux

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Enriched: decoding document...
Indenting...
Note: file is write protected
Whitespace mode enabled in current buffer
You can run the command ‘whitespace-mode’ with M-x whit-m RET
Whitespace mode enabled in current buffer

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-wide-int
 --with-modules 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
XPM JPEG TIFF GIF PNG RSVG IMAGEMAGICK SOUND GPM DBUS GSETTINGS GLIB
NOTIFY ACL GNUTLS LIBXML2 FREETYPE M17N_FLT LIBOTF XFT ZLIB
TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD LCMS2

Important settings:
  value of $LC_MESSAGES: 
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: Text

Minor modes in effect:
  whitespace-mode: t
  enriched-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  use-hard-newlines: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny seq byte-opt gv
bytecomp byte-compile cconv cl-loaddefs cl-lib dired dired-loaddefs
format-spec rfc822 mml easymenu mml-sec password-cache epa derived epg
epg-config gnus-util rmail rmail-loaddefs mm-decode mm-bodies mm-encode
mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail rfc2047
rfc2045 ietf-drums mm-util mail-prsvr mail-utils whitespace disp-table
enriched elec-pair time-date mule-util tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads dbusbind inotify lcms2 dynamic-setting
system-font-setting font-render-setting move-toolbar gtk x-toolkit x
multi-tty make-network-process emacs)

Memory information:
((conses 16 101223 9021)
 (symbols 48 20550 1)
 (miscs 40 62 154)
 (strings 32 29069 1125)
 (string-bytes 1 778480)
 (vectors 16 14213)
 (vector-slots 8 506032 11338)
 (floats 8 49 68)
 (intervals 56 902 0)
 (buffers 992 12))