HTML with inline script can cause an error in mhtml-syntax-propertize. Recipe from emacs -Q: Visit a new file "index.html" and insert these contents: it's Put the cursor after the zero and type a semicolon. An error is signalled. (Note the "unmatched" apostrophe in the HTML body.) Errors: Error during redisplay: (jit-lock-function 1) signaled (wrong-type-argument number-or-marker-p nil) mhtml-syntax-propertize: Wrong type argument: number-or-marker-p, nil Backtrace: Debugger entered--Lisp error: (wrong-type-argument number-or-marker-p nil) sgml--syntax-propertize-ppss(86) mhtml-syntax-propertize(33 107) syntax-propertize(50) syntax-ppss() electric-indent-post-self-insert-function() self-insert-command(1 59) funcall-interactively(self-insert-command 1 59) call-interactively(self-insert-command nil nil) command-execute(self-insert-command) In GNU Emacs 27.0.50 (build 6, x86_64-w64-mingw32) of 2019-11-24 built on MACHINE Repository revision: 5a3e96b17c2a948ac952295962dc6e281ec5cad5 Repository branch: master Windowing system distributor 'Microsoft Corp.', version 10.0.19025 System Description: Microsoft Windows 10 Pro (v10.0.1903.19025.1051) Recent messages: For information about GNU Emacs and the GNU system, type C-h C-a. (New file) Mark set Error during redisplay: (jit-lock-function 1) signaled (wrong-type-argument number-or-marker-p nil) mhtml-syntax-propertize: Wrong type argument: number-or-marker-p, nil Configured using: 'configure --config-cache --with-modules --without-pop --without-dbus --without-gconf --without-gsettings CFLAGS=-O2' Configured features: XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY W32NOTIFY ACL GNUTLS LIBXML2 HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS MODULES THREADS JSON PDUMPER LCMS2 GMP Important settings: value of $LANG: ENG locale-coding-system: cp1252 Major mode: HTML+JS Minor modes in effect: tooltip-mode: t global-eldoc-mode: t electric-indent-mode: t mouse-wheel-mode: t tool-bar-mode: 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 line-number-mode: t transient-mark-mode: t Load-path shadows: None found. Features: (shadow sort mail-extr emacsbug message rmc dired dired-loaddefs rfc822 mml mml-sec epa derived epg epg-config mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail vc-git diff-mode easy-mmode mhtml-mode css-mode smie eww mm-url gnus nnheader gnus-util rmail rmail-loaddefs rfc2047 rfc2045 ietf-drums time-date mail-utils wid-edit mm-util mail-prsvr thingatpt url-queue url url-proxy url-privacy url-expand url-methods url-history mailcap shr text-property-search url-cookie url-domsuf url-util url-parse auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs password-cache url-vars puny svg xml browse-url format-spec color js json subr-x map imenu cc-mode cc-fonts easymenu cc-guess cc-menus cc-cmds cc-styles cc-align cc-engine cc-vars cc-defs sgml-mode seq byte-opt gv bytecomp byte-compile cconv dom cl-loaddefs cl-lib tooltip eldoc electric uniquify ediff-hook vc-hooks lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe tabulated-list replace newcomment text-mode elisp-mode lisp-mode prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer select scroll-bar mouse jit-lock font-lock syntax facemenu font-core term/tty-colors frame minibuffer 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 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 w32notify w32 lcms2 multi-tty make-network-process emacs) Memory information: ((conses 16 113316 8380) (symbols 48 13210 1) (strings 32 40080 2328) (string-bytes 1 1310957) (vectors 16 18724) (vector-slots 8 235664 6880) (floats 8 204 73) (intervals 56 264 0) (buffers 1000 12))