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+;;; lazy-lock.el --- lazy demand-driven fontification for fast Font Lock mode
+
+;; Copyright (C) 1994, 1995, 1996, 1997, 1998, 2001
+;;   Free Software Foundation, Inc.
+
+;; Author: Simon Marshall <simon@gnu.org>
+;; Maintainer: FSF
+;; Keywords: faces files
+;; Version: 2.11
+
+;; This file is part of GNU Emacs.
+
+;; GNU Emacs is free software; you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation; either version 2, or (at your option)
+;; any later version.
+
+;; GNU Emacs is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with GNU Emacs; see the file COPYING.  If not, write to the
+;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+;; Boston, MA 02111-1307, USA.
+
+;;; Commentary:
+
+;; Purpose:
+;;
+;; Lazy Lock mode is a Font Lock support mode.
+;; It makes visiting buffers in Font Lock mode faster by making fontification
+;; be demand-driven, deferred and stealthy, so that fontification only occurs
+;; when, and where, necessary.
+;;
+;; See caveats and feedback below.
+;; See also the fast-lock package.  (But don't use them at the same time!)
+
+;; Installation:
+;;
+;; Put in your ~/.emacs:
+;;
+;; (setq font-lock-support-mode 'lazy-lock-mode)
+;;
+;; Start up a new Emacs and use font-lock as usual (except that you can use the
+;; so-called "gaudier" fontification regexps on big files without frustration).
+;;
+;; In a buffer (which has `font-lock-mode' enabled) which is at least
+;; `lazy-lock-minimum-size' characters long, buffer fontification will not
+;; occur and only the visible portion of the buffer will be fontified.  Motion
+;; around the buffer will fontify those visible portions not previously
+;; fontified.  If stealth fontification is enabled, buffer fontification will
+;; occur in invisible parts of the buffer after `lazy-lock-stealth-time'
+;; seconds of idle time.  If on-the-fly fontification is deferred, on-the-fly
+;; fontification will occur after `lazy-lock-defer-time' seconds of idle time.
+
+;; User-visible differences with version 1:
+;;
+;; - Version 2 can defer on-the-fly fontification.  Therefore you need not, and
+;; should not, use defer-lock.el with this version of lazy-lock.el.
+;;
+;; A number of variables have changed meaning:
+;;
+;; - A value of nil for the variable `lazy-lock-minimum-size' means never turn
+;; on demand-driven fontification.  In version 1 this meant always turn on
+;; demand-driven fontification.  If you really want demand-driven fontification
+;; regardless of buffer size, set this variable to 0.
+;;
+;; - The variable `lazy-lock-stealth-lines' cannot have a nil value.  In
+;; version 1 this meant use `window-height' as the maximum number of lines to
+;; fontify as a stealth chunk.  This makes no sense; stealth fontification is
+;; of a buffer, not a window.
+
+;; Implementation differences with version 1:
+;;
+;; - Version 1 of lazy-lock.el is a bit of a hack.  Version 1 demand-driven
+;; fontification, the core feature of lazy-lock.el, is implemented by placing a
+;; function on `post-command-hook'.  This function fontifies where necessary,
+;; i.e., where a window scroll has occurred.  However, there are a number of
+;; problems with using `post-command-hook':
+;;
+;; (a) As the name suggests, `post-command-hook' is run after every command,
+;;     i.e., frequently and regardless of whether scrolling has occurred.
+;; (b) Scrolling can occur during a command, when `post-command-hook' is not
+;;     run, i.e., it is not necessarily run after scrolling has occurred.
+;; (c) When `post-command-hook' is run, there is nothing to suggest where
+;;     scrolling might have occurred, i.e., which windows have scrolled.
+;;
+;; Thus lazy-lock.el's function is called almost as often as possible, usually
+;; when it need not be called, yet it is not always called when it is needed.
+;; Also, lazy-lock.el's function must check each window to see if a scroll has
+;; occurred there.  Worse still, lazy-lock.el's function must fontify a region
+;; twice as large as necessary to make sure the window is completely fontified.
+;; Basically, `post-command-hook' is completely inappropriate for lazy-lock.el.
+;;
+;; Ideally, we want to attach lazy-lock.el's function to a hook that is run
+;; only when scrolling occurs, e.g., `window-start' has changed, and tells us
+;; as much information as we need, i.e., the window and its new buffer region.
+;; Richard Stallman implemented a `window-scroll-functions' for Emacs 19.30.
+;; Functions on it are run when `window-start' has changed, and are supplied
+;; with the window and the window's new `window-start' position.  (It would be
+;; better if it also supplied the window's new `window-end' position, but that
+;; is calculated as part of the redisplay process, and the functions on
+;; `window-scroll-functions' are run before redisplay has finished.)  Thus, the
+;; hook deals with the above problems (a), (b) and (c).
+;;
+;; If only life was that easy.  Version 2 demand-driven fontification is mostly
+;; implemented by placing a function on `window-scroll-functions'.  However,
+;; not all scrolling occurs when `window-start' has changed.  A change in
+;; window size, e.g., via C-x 1, or a significant deletion, e.g., of a number
+;; of lines, causes text previously invisible (i.e., after `window-end') to
+;; become visible without changing `window-start'.  Arguably, these events are
+;; not scrolling events, but fontification must occur for lazy-lock.el to work.
+;; Hooks `window-size-change-functions' and `redisplay-end-trigger-functions'
+;; were added for these circumstances.
+;;
+;; (Ben Wing thinks these hooks are "horribly horribly kludgy", and implemented
+;; a `pre-idle-hook', a `mother-of-all-post-command-hooks', for XEmacs 19.14.
+;; He then hacked up a version 1 lazy-lock.el to use `pre-idle-hook' rather
+;; than `post-command-hook'.  Whereas functions on `post-command-hook' are
+;; called almost as often as possible, functions on `pre-idle-hook' really are
+;; called as often as possible, even when the mouse moves and, on some systems,
+;; while XEmacs is idle.  Thus, the hook deals with the above problem (b), but
+;; unfortunately it makes (a) worse and does not address (c) at all.
+;;
+;; I freely admit that `redisplay-end-trigger-functions' and, to a much lesser
+;; extent, `window-size-change-functions' are not pretty.  However, I feel that
+;; a `window-scroll-functions' feature is cleaner than a `pre-idle-hook', and
+;; the result is faster and smaller, less intrusive and more targeted, code.
+;; Since `pre-idle-hook' is pretty much like `post-command-hook', there is no
+;; point in making this version of lazy-lock.el work with it.  Anyway, that's
+;; Lit 30 of my humble opinion.
+;;
+;; - Version 1 stealth fontification is also implemented by placing a function
+;; on `post-command-hook'.  This function waits for a given amount of time,
+;; and, if Emacs remains idle, fontifies where necessary.  Again, there are a
+;; number of problems with using `post-command-hook':
+;;
+;; (a) Functions on `post-command-hook' are run sequentially, so this function
+;;     can interfere with other functions on the hook, and vice versa.
+;; (b) This function waits for a given amount of time, so it can interfere with
+;;     various features that are dealt with by Emacs after a command, e.g.,
+;;     region highlighting, asynchronous updating and keystroke echoing.
+;; (c) Fontification may be required during a command, when `post-command-hook'
+;;     is not run.  (Version 2 deferred fontification only.)
+;;
+;; Again, `post-command-hook' is completely inappropriate for lazy-lock.el.
+;; Richard Stallman and Morten Welinder implemented internal Timers and Idle
+;; Timers for Emacs 19.31.  Functions can be run independently at given times
+;; or after given amounts of idle time.  Thus, the feature deals with the above
+;; problems (a), (b) and (c).  Version 2 deferral and stealth are implemented
+;; by functions on Idle Timers.  (A function on XEmacs' `pre-idle-hook' is
+;; similar to an Emacs Idle Timer function with a fixed zero second timeout.)
+
+;; - Version 1 has the following problems (relative to version 2):
+;;
+;; (a) It is slow when it does its job.
+;; (b) It does not always do its job when it should.
+;; (c) It slows all interaction (when it doesn't need to do its job).
+;; (d) It interferes with other package functions on `post-command-hook'.
+;; (e) It interferes with Emacs things within the read-eval loop.
+;;
+;; Ben's hacked-up lazy-lock.el 1.14 almost solved (b) but made (c) worse.
+;;
+;; - Version 2 has the following additional features (relative to version 1):
+;;
+;; (a) It can defer fontification (both on-the-fly and on-scrolling).
+;; (b) It can fontify contextually (syntactically true on-the-fly).
+
+;; Caveats:
+;;
+;; Lazy Lock mode does not work efficiently with Outline mode.
+;; This is because when in Outline mode, although text may be not visible to
+;; you in the window, the text is visible to Emacs Lisp code (not surprisingly)
+;; and Lazy Lock fontifies it mercilessly.  Maybe it will be fixed one day.
+;;
+;; Because buffer text is not necessarily fontified, other packages that expect
+;; buffer text to be fontified in Font Lock mode either might not work as
+;; expected, or might not display buffer text as expected.  An example of the
+;; latter is `occur', which copies lines of buffer text into another buffer.
+;;
+;; In Emacs 19.30, Lazy Lock mode does not ensure that an existing buffer is
+;; fontified if it is made visible via a minibuffer-less command that replaces
+;; an existing window's buffer (e.g., via the Buffers menu).  Upgrade!
+;;
+;; In Emacs 19.30, Lazy Lock mode does not work well with Transient Mark mode
+;; or modes based on Comint mode (e.g., Shell mode), and also interferes with
+;; the echoing of keystrokes in the minibuffer.  This is because of the way
+;; deferral and stealth have to be implemented for Emacs 19.30.  Upgrade!
+;;
+;; Currently XEmacs does not have the features to support this version of
+;; lazy-lock.el.  Maybe it will one day.
+
+;; History:
+;;
+;; 1.15--2.00:
+;; - Rewrite for Emacs 19.30 and the features rms added to support lazy-lock.el
+;;   so that it could work correctly and efficiently.
+;; - Many thanks to those who reported bugs, fixed bugs, made suggestions or
+;;   otherwise contributed in the version 1 cycle; Jari Aalto, Kevin Broadey,
+;;   Ulrik Dickow, Bill Dubuque, Bob Glickstein, Boris Goldowsky,
+;;   Jonas Jarnestrom, David Karr, Michael Kifer, Erik Naggum, Rick Sladkey,
+;;   Jim Thompson, Ben Wing, Ilya Zakharevich, and Richard Stallman.
+;; 2.00--2.01:
+;; - Made `lazy-lock-fontify-after-command' always `sit-for' and so redisplay
+;; - Use `buffer-name' not `buffer-live-p' (Bill Dubuque hint)
+;; - Made `lazy-lock-install' do `add-to-list' not `setq' of `current-buffer'
+;; - Made `lazy-lock-fontify-after-install' loop over buffer list
+;; - Made `lazy-lock-arrange-before-change' to arrange `window-end' triggering
+;; - Made `lazy-lock-let-buffer-state' wrap both `befter-change-functions'
+;; - Made `lazy-lock-fontify-region' do `condition-case' (Hyman Rosen report)
+;; 2.01--2.02:
+;; - Use `buffer-live-p' as `buffer-name' can barf (Richard Stanton report)
+;; - Made `lazy-lock-install' set `font-lock-fontified' (Kevin Davidson report)
+;; - Made `lazy-lock-install' add hooks only if needed
+;; - Made `lazy-lock-unstall' add `font-lock-after-change-function' if needed
+;; 2.02--2.03:
+;; - Made `lazy-lock-fontify-region' do `condition-case' for `quit' too
+;; - Made `lazy-lock-mode' respect the value of `font-lock-inhibit-thing-lock'
+;; - Added `lazy-lock-after-unfontify-buffer'
+;; - Removed `lazy-lock-fontify-after-install' hack
+;; - Made `lazy-lock-fontify-after-scroll' not `set-buffer' to `window-buffer'
+;; - Made `lazy-lock-fontify-after-trigger' not `set-buffer' to `window-buffer'
+;; - Made `lazy-lock-fontify-after-idle' be interruptible (Scott Burson hint)
+;; 2.03--2.04:
+;; - Rewrite for Emacs 19.31 idle timers
+;; - Renamed `buffer-windows' to `get-buffer-window-list'
+;; - Removed `buffer-live-p'
+;; - Made `lazy-lock-defer-after-change' always save `current-buffer'
+;; - Made `lazy-lock-fontify-after-defer' just process buffers
+;; - Made `lazy-lock-install-hooks' add hooks correctly (Kevin Broadey report)
+;; - Made `lazy-lock-install' cope if `lazy-lock-defer-time' is a list
+;; 2.04--2.05:
+;; - Rewrite for Common Lisp macros
+;; - Added `do-while' macro
+;; - Renamed `lazy-lock-let-buffer-state' macro to `save-buffer-state'
+;; - Returned `lazy-lock-fontify-after-install' hack (Darren Hall hint)
+;; - Added `lazy-lock-defer-on-scrolling' functionality (Scott Byer hint)
+;; - Made `lazy-lock-mode' wrap `font-lock-support-mode'
+;; 2.05--2.06:
+;; - Made `lazy-lock-fontify-after-defer' swap correctly (Scott Byer report)
+;; 2.06--2.07:
+;; - Added `lazy-lock-stealth-load' functionality (Rob Hooft hint)
+;; - Made `lazy-lock-unstall' call `lazy-lock-fontify-region' if needed
+;; - Made `lazy-lock-mode' call `lazy-lock-unstall' only if needed
+;; - Made `lazy-lock-defer-after-scroll' do `set-window-redisplay-end-trigger'
+;; - Added `lazy-lock-defer-contextually' functionality
+;; - Added `lazy-lock-defer-on-the-fly' from `lazy-lock-defer-time'
+;; - Renamed `lazy-lock-defer-driven' to `lazy-lock-defer-on-scrolling'
+;; - Removed `lazy-lock-submit-bug-report' and bade farewell
+;; 2.07--2.08:
+;; - Made `lazy-lock-fontify-conservatively' fontify around `window-point'
+;; - Made `save-buffer-state' wrap `inhibit-point-motion-hooks'
+;; - Added Custom support
+;; 2.08--2.09:
+;; - Removed `byte-*' variables from `eval-when-compile' (Erik Naggum hint)
+;; - Made various wrapping `inhibit-point-motion-hooks' (Vinicius Latorre hint)
+;; - Made `lazy-lock-fontify-after-idle' wrap `minibuffer-auto-raise'
+;; - Made `lazy-lock-fontify-after-defer' paranoid about deferred buffers
+;; 2.09--2.10:
+;; - Use `window-end' UPDATE arg for Emacs 20.4 and later.
+;; - Made deferral `widen' before unfontifying (Dan Nicolaescu report)
+;; - Use `lazy-lock-fontify-after-visage' for hideshow.el (Dan Nicolaescu hint)
+;; - Use `other' widget where possible (Andreas Schwab fix)
+;; 2.10--2.11:
+;; - Used `with-temp-message' where possible to make messages temporary.
+
+;;; Code:
+
+(require 'font-lock)
+
+(eval-when-compile
+ ;; We don't do this at the top-level as we only use non-autoloaded macros.
+ (require 'cl)
+ ;;
+ ;; We use this to preserve or protect things when modifying text properties.
+ (defmacro save-buffer-state (varlist &rest body)
+   "Bind variables according to VARLIST and eval BODY restoring buffer state."
+   `(let* (,@(append varlist
+		   '((modified (buffer-modified-p))
+		     (buffer-undo-list t)
+		     (inhibit-read-only t)
+		     (inhibit-point-motion-hooks t)
+		     (inhibit-modification-hooks t)
+		     deactivate-mark
+		     buffer-file-name
+		     buffer-file-truename)))
+     ,@body
+     (when (and (not modified) (buffer-modified-p))
+       (restore-buffer-modified-p nil))))
+ (put 'save-buffer-state 'lisp-indent-function 1)
+ ;;
+ ;; We use this for clarity and speed.  Naughty but nice.
+ (defmacro do-while (test &rest body)
+   "(do-while TEST BODY...): eval BODY... and repeat if TEST yields non-nil.
+The order of execution is thus BODY, TEST, BODY, TEST and so on
+until TEST returns nil."
+   `(while (progn ,@body ,test)))
+ (put 'do-while 'lisp-indent-function (get 'while 'lisp-indent-function)))
+
+(defvar lazy-lock-mode nil)			; Whether we are turned on.
+(defvar lazy-lock-buffers nil)			; For deferral.
+(defvar lazy-lock-timers (cons nil nil))	; For deferral and stealth.
+
+;; User Variables:
+
+(defcustom lazy-lock-minimum-size 25600
+  "*Minimum size of a buffer for demand-driven fontification.
+On-demand fontification occurs if the buffer size is greater than this value.
+If nil, means demand-driven fontification is never performed.
+If a list, each element should be a cons pair of the form (MAJOR-MODE . SIZE),
+where MAJOR-MODE is a symbol or t (meaning the default).  For example:
+ ((c-mode . 25600) (c++-mode . 25600) (rmail-mode . 1048576))
+means that the minimum size is 25K for buffers in C or C++ modes, one megabyte
+for buffers in Rmail mode, and size is irrelevant otherwise.
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "none" nil)
+		 (integer :tag "size")
+		 (repeat :menu-tag "mode specific" :tag "mode specific"
+			 :value ((t . nil))
+			 (cons :tag "Instance"
+			       (radio :tag "Mode"
+				      (const :tag "all" t)
+				      (symbol :tag "name"))
+			       (radio :tag "Size"
+				      (const :tag "none" nil)
+				      (integer :tag "size")))))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-defer-on-the-fly t
+  "*If non-nil, means fontification after a change should be deferred.
+If nil, means on-the-fly fontification is performed.  This means when changes
+occur in the buffer, those areas are immediately fontified.
+If a list, it should be a list of `major-mode' symbol names for which deferred
+fontification should occur.  The sense of the list is negated if it begins with
+`not'.  For example:
+ (c-mode c++-mode)
+means that on-the-fly fontification is deferred for buffers in C and C++ modes
+only, and deferral does not occur otherwise.
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "never" nil)
+		 (const :tag "always" t)
+		 (set :menu-tag "mode specific" :tag "modes"
+		      :value (not)
+		      (const :tag "Except" not)
+		      (repeat :inline t (symbol :tag "mode"))))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-defer-on-scrolling nil
+  "*If non-nil, means fontification after a scroll should be deferred.
+If nil, means demand-driven fontification is performed.  This means when
+scrolling into unfontified areas of the buffer, those areas are immediately
+fontified.  Thus scrolling never presents unfontified areas.  However, since
+fontification occurs during scrolling, scrolling may be slow.
+If t, means defer-driven fontification is performed.  This means fontification
+of those areas is deferred.  Thus scrolling may present momentarily unfontified
+areas.  However, since fontification does not occur during scrolling, scrolling
+will be faster than demand-driven fontification.
+If any other value, e.g., `eventually', means demand-driven fontification is
+performed until the buffer is fontified, then buffer fontification becomes
+defer-driven.  Thus scrolling never presents unfontified areas until the buffer
+is first fontified, after which subsequent scrolling may present future buffer
+insertions momentarily unfontified.  However, since fontification does not
+occur during scrolling after the buffer is first fontified, scrolling will
+become faster.  (But, since contextual changes continually occur, such a value
+makes little sense if `lazy-lock-defer-contextually' is non-nil.)
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "never" nil)
+		 (const :tag "always" t)
+		 (other :tag "eventually" eventually))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-defer-contextually 'syntax-driven
+  "*If non-nil, means deferred fontification should be syntactically true.
+If nil, means deferred fontification occurs only on those lines modified.  This
+means where modification on a line causes syntactic change on subsequent lines,
+those subsequent lines are not refontified to reflect their new context.
+If t, means deferred fontification occurs on those lines modified and all
+subsequent lines.  This means those subsequent lines are refontified to reflect
+their new syntactic context, either immediately or when scrolling into them.
+If any other value, e.g., `syntax-driven', means deferred syntactically true
+fontification occurs only if syntactic fontification is performed using the
+buffer mode's syntax table, i.e., only if `font-lock-keywords-only' is nil.
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "never" nil)
+		 (const :tag "always" t)
+		 (other :tag "syntax-driven" syntax-driven))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-defer-time
+  (if (featurep 'lisp-float-type) (/ (float 1) (float 4)) 1)
+  "*Time in seconds to delay before beginning deferred fontification.
+Deferred fontification occurs if there is no input within this time.
+If nil, means fontification is never deferred, regardless of the values of the
+variables `lazy-lock-defer-on-the-fly', `lazy-lock-defer-on-scrolling' and
+`lazy-lock-defer-contextually'.
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "never" nil)
+		 (number :tag "seconds"))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-stealth-time 30
+  "*Time in seconds to delay before beginning stealth fontification.
+Stealth fontification occurs if there is no input within this time.
+If nil, means stealth fontification is never performed.
+
+The value of this variable is used when Lazy Lock mode is turned on."
+  :type '(choice (const :tag "never" nil)
+		 (number :tag "seconds"))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-stealth-lines (if font-lock-maximum-decoration 100 250)
+  "*Maximum size of a chunk of stealth fontification.
+Each iteration of stealth fontification can fontify this number of lines.
+To speed up input response during stealth fontification, at the cost of stealth
+taking longer to fontify, you could reduce the value of this variable."
+  :type '(integer :tag "lines")
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-stealth-load
+  (if (condition-case nil (load-average) (error)) 200)
+  "*Load in percentage above which stealth fontification is suspended.
+Stealth fontification pauses when the system short-term load average (as
+returned by the function `load-average' if supported) goes above this level,
+thus reducing the demand that stealth fontification makes on the system.
+If nil, means stealth fontification is never suspended.
+To reduce machine load during stealth fontification, at the cost of stealth
+taking longer to fontify, you could reduce the value of this variable.
+See also `lazy-lock-stealth-nice'."
+  :type (if (condition-case nil (load-average) (error))
+	    '(choice (const :tag "never" nil)
+		     (integer :tag "load"))
+	  '(const :format "%t: unsupported\n" nil))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-stealth-nice
+  (if (featurep 'lisp-float-type) (/ (float 1) (float 8)) 1)
+  "*Time in seconds to pause between chunks of stealth fontification.
+Each iteration of stealth fontification is separated by this amount of time,
+thus reducing the demand that stealth fontification makes on the system.
+If nil, means stealth fontification is never paused.
+To reduce machine load during stealth fontification, at the cost of stealth
+taking longer to fontify, you could increase the value of this variable.
+See also `lazy-lock-stealth-load'."
+  :type '(choice (const :tag "never" nil)
+		 (number :tag "seconds"))
+  :group 'lazy-lock)
+
+(defcustom lazy-lock-stealth-verbose
+  (if (featurep 'lisp-float-type)
+      (and (not lazy-lock-defer-contextually) (not (null font-lock-verbose))))
+  "*If non-nil, means stealth fontification should show status messages."
+  :type 'boolean
+  :group 'lazy-lock)
+
+;; User Functions:
+
+;;;###autoload
+(defun lazy-lock-mode (&optional arg)
+  "Toggle Lazy Lock mode.
+With arg, turn Lazy Lock mode on if and only if arg is positive.  Enable it
+automatically in your `~/.emacs' by:
+
+ (setq font-lock-support-mode 'lazy-lock-mode)
+
+For a newer font-lock support mode with similar functionality, see
+`jit-lock-mode'.  Eventually, Lazy Lock mode will be deprecated in
+JIT Lock's favor.
+
+When Lazy Lock mode is enabled, fontification can be lazy in a number of ways:
+
+- Demand-driven buffer fontification if `lazy-lock-minimum-size' is non-nil.
+  This means initial fontification does not occur if the buffer is greater than
+  `lazy-lock-minimum-size' characters in length.  Instead, fontification occurs
+  when necessary, such as when scrolling through the buffer would otherwise
+  reveal unfontified areas.  This is useful if buffer fontification is too slow
+  for large buffers.
+
+- Deferred scroll fontification if `lazy-lock-defer-on-scrolling' is non-nil.
+  This means demand-driven fontification does not occur as you scroll.
+  Instead, fontification is deferred until after `lazy-lock-defer-time' seconds
+  of Emacs idle time, while Emacs remains idle.  This is useful if
+  fontification is too slow to keep up with scrolling.
+
+- Deferred on-the-fly fontification if `lazy-lock-defer-on-the-fly' is non-nil.
+  This means on-the-fly fontification does not occur as you type.  Instead,
+  fontification is deferred until after `lazy-lock-defer-time' seconds of Emacs
+  idle time, while Emacs remains idle.  This is useful if fontification is too
+  slow to keep up with your typing.
+
+- Deferred context fontification if `lazy-lock-defer-contextually' is non-nil.
+  This means fontification updates the buffer corresponding to true syntactic
+  context, after `lazy-lock-defer-time' seconds of Emacs idle time, while Emacs
+  remains idle.  Otherwise, fontification occurs on modified lines only, and
+  subsequent lines can remain fontified corresponding to previous syntactic
+  contexts.  This is useful where strings or comments span lines.
+
+- Stealthy buffer fontification if `lazy-lock-stealth-time' is non-nil.
+  This means remaining unfontified areas of buffers are fontified if Emacs has
+  been idle for `lazy-lock-stealth-time' seconds, while Emacs remains idle.
+  This is useful if any buffer has any deferred fontification.
+
+Basic Font Lock mode on-the-fly fontification behaviour fontifies modified
+lines only.  Thus, if `lazy-lock-defer-contextually' is non-nil, Lazy Lock mode
+on-the-fly fontification may fontify differently, albeit correctly.  In any
+event, to refontify some lines you can use \\[font-lock-fontify-block].
+
+Stealth fontification only occurs while the system remains unloaded.
+If the system load rises above `lazy-lock-stealth-load' percent, stealth
+fontification is suspended.  Stealth fontification intensity is controlled via
+the variable `lazy-lock-stealth-nice' and `lazy-lock-stealth-lines', and
+verbosity is controlled via the variable `lazy-lock-stealth-verbose'."
+  (interactive "P")
+  (let* ((was-on lazy-lock-mode)
+	 (now-on (unless (memq 'lazy-lock-mode font-lock-inhibit-thing-lock)
+		   (if arg (> (prefix-numeric-value arg) 0) (not was-on)))))
+    (cond ((and now-on (not font-lock-mode))
+	   ;; Turned on `lazy-lock-mode' rather than `font-lock-mode'.
+	   (let ((font-lock-support-mode 'lazy-lock-mode))
+	     (font-lock-mode t)))
+	  (now-on
+	   ;; Turn ourselves on.
+	   (set (make-local-variable 'lazy-lock-mode) t)
+	   (lazy-lock-install))
+	  (was-on
+	   ;; Turn ourselves off.
+	   (set (make-local-variable 'lazy-lock-mode) nil)
+	   (lazy-lock-unstall)))))
+
+;;;###autoload
+(defun turn-on-lazy-lock ()
+  "Unconditionally turn on Lazy Lock mode."
+  (lazy-lock-mode t))
+
+(defun lazy-lock-install ()
+  (let ((min-size (font-lock-value-in-major-mode lazy-lock-minimum-size))
+	(defer-change (and lazy-lock-defer-time lazy-lock-defer-on-the-fly))
+	(defer-scroll (and lazy-lock-defer-time lazy-lock-defer-on-scrolling))
+	(defer-context (and lazy-lock-defer-time lazy-lock-defer-contextually
+			    (or (eq lazy-lock-defer-contextually t)
+				(null font-lock-keywords-only)))))
+    ;;
+    ;; Tell Font Lock whether Lazy Lock will do fontification.
+    (make-local-variable 'font-lock-fontified)
+    (setq font-lock-fontified (and min-size (>= (buffer-size) min-size)))
+    ;;
+    ;; Add the text properties and fontify.
+    (if (not font-lock-fontified)
+	(lazy-lock-after-fontify-buffer)
+      ;; Make sure we fontify in any existing windows showing the buffer.
+      (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)))
+	(lazy-lock-after-unfontify-buffer)
+	(while windows
+	  (lazy-lock-fontify-conservatively (car windows))
+	  (setq windows (cdr windows)))))
+    ;;
+    ;; Add the fontification hooks.
+    (lazy-lock-install-hooks
+     font-lock-fontified
+     (cond ((eq (car-safe defer-change) 'not)
+	    (not (memq major-mode (cdr defer-change))))
+	   ((listp defer-change)
+	    (memq major-mode defer-change))
+	   (t
+	    defer-change))
+     (eq defer-scroll t)
+     defer-context)
+    ;;
+    ;; Add the fontification timers.
+    (lazy-lock-install-timers
+     (if (or defer-change defer-scroll defer-context) lazy-lock-defer-time)
+     lazy-lock-stealth-time)))
+
+(defun lazy-lock-install-hooks (fontifying
+				defer-change defer-scroll defer-context)
+  ;;
+  ;; Add hook if lazy-lock.el is fontifying on scrolling or is deferring.
+  (when (or fontifying defer-change defer-scroll defer-context)
+    (add-hook 'window-scroll-functions (if defer-scroll
+					   'lazy-lock-defer-after-scroll
+					 'lazy-lock-fontify-after-scroll)
+	      nil t))
+  ;;
+  ;; Add hook if lazy-lock.el is fontifying and is not deferring changes.
+  (when (and fontifying (not defer-change) (not defer-context))
+    (add-hook 'before-change-functions 'lazy-lock-arrange-before-change nil t))
+  ;;
+  ;; Replace Font Lock mode hook.
+  (remove-hook 'after-change-functions 'font-lock-after-change-function t)
+  (add-hook 'after-change-functions
+	    (cond ((and defer-change defer-context)
+		   'lazy-lock-defer-rest-after-change)
+		  (defer-change
+		   'lazy-lock-defer-line-after-change)
+		  (defer-context
+		   'lazy-lock-fontify-rest-after-change)
+		  (t
+		   'lazy-lock-fontify-line-after-change))
+	    nil t)
+  ;;
+  ;; Add package-specific hook.
+  (add-hook 'outline-view-change-hook 'lazy-lock-fontify-after-visage nil t)
+  (add-hook 'hs-hide-hook 'lazy-lock-fontify-after-visage nil t))
+
+(defun lazy-lock-install-timers (dtime stime)
+  ;; Schedule or re-schedule the deferral and stealth timers.
+  ;; The layout of `lazy-lock-timers' is:
+  ;;  ((DEFER-TIME . DEFER-TIMER) (STEALTH-TIME . STEALTH-TIMER)
+  ;; If an idle timeout has changed, cancel the existing idle timer (if there
+  ;; is one) and schedule a new one (if the new idle timeout is non-nil).
+  (unless (eq dtime (car (car lazy-lock-timers)))
+    (let ((defer (car lazy-lock-timers)))
+      (when (cdr defer)
+	(cancel-timer (cdr defer)))
+      (setcar lazy-lock-timers (cons dtime (and dtime
+	      (run-with-idle-timer dtime t 'lazy-lock-fontify-after-defer))))))
+  (unless (eq stime (car (cdr lazy-lock-timers)))
+    (let ((stealth (cdr lazy-lock-timers)))
+      (when (cdr stealth)
+	(cancel-timer (cdr stealth)))
+      (setcdr lazy-lock-timers (cons stime (and stime
+	      (run-with-idle-timer stime t 'lazy-lock-fontify-after-idle)))))))
+
+(defun lazy-lock-unstall ()
+  ;;
+  ;; If Font Lock mode is still enabled, make sure that the buffer is
+  ;; fontified, and reinstall its hook.  We must do this first.
+  (when font-lock-mode
+    (when (lazy-lock-unfontified-p)
+      (let ((verbose (if (numberp font-lock-verbose)
+			 (> (buffer-size) font-lock-verbose)
+		       font-lock-verbose)))
+	(with-temp-message
+	    (when verbose
+	      (format "Fontifying %s..." (buffer-name)))
+	  ;; Make sure we fontify etc. in the whole buffer.
+	  (save-restriction
+	    (widen)
+	    (lazy-lock-fontify-region (point-min) (point-max))))))
+    (add-hook 'after-change-functions 'font-lock-after-change-function nil t))
+  ;;
+  ;; Remove the text properties.
+  (lazy-lock-after-unfontify-buffer)
+  ;;
+  ;; Remove the fontification hooks.
+  (remove-hook 'window-scroll-functions 'lazy-lock-fontify-after-scroll t)
+  (remove-hook 'window-scroll-functions 'lazy-lock-defer-after-scroll t)
+  (remove-hook 'before-change-functions 'lazy-lock-arrange-before-change t)
+  (remove-hook 'after-change-functions 'lazy-lock-fontify-line-after-change t)
+  (remove-hook 'after-change-functions 'lazy-lock-fontify-rest-after-change t)
+  (remove-hook 'after-change-functions 'lazy-lock-defer-line-after-change t)
+  (remove-hook 'after-change-functions 'lazy-lock-defer-rest-after-change t)
+  (remove-hook 'outline-view-change-hook 'lazy-lock-fontify-after-visage t)
+  (remove-hook 'hs-hide-hook 'lazy-lock-fontify-after-visage t))
+
+;; Hook functions.
+
+;; Lazy Lock mode intervenes when (1) a previously invisible buffer region
+;; becomes visible, i.e., for demand- or defer-driven on-the-scroll
+;; fontification, (2) a buffer modification occurs, i.e., for defer-driven
+;; on-the-fly fontification, (3) Emacs becomes idle, i.e., for fontification of
+;; deferred fontification and stealth fontification, and (4) other special
+;; occasions.
+
+;; 1.  There are three ways whereby this can happen.
+;;
+;; (a) Scrolling the window, either explicitly (e.g., `scroll-up') or
+;;     implicitly (e.g., `search-forward').  Here, `window-start' changes.
+;;     Fontification occurs by adding `lazy-lock-fontify-after-scroll' (for
+;;     demand-driven fontification) or `lazy-lock-defer-after-scroll' (for
+;;     defer-driven fontification) to the hook `window-scroll-functions'.
+
+(defun lazy-lock-fontify-after-scroll (window window-start)
+  ;; Called from `window-scroll-functions'.
+  ;; Fontify WINDOW from WINDOW-START following the scroll.
+  (let ((inhibit-point-motion-hooks t))
+    (lazy-lock-fontify-region window-start (window-end window t)))
+  ;; A prior deletion that did not cause scrolling, followed by a scroll, would
+  ;; result in an unnecessary trigger after this if we did not cancel it now.
+  (set-window-redisplay-end-trigger window nil))
+
+(defun lazy-lock-defer-after-scroll (window window-start)
+  ;; Called from `window-scroll-functions'.
+  ;; Defer fontification following the scroll.  Save the current buffer so that
+  ;; we subsequently fontify in all windows showing the buffer.
+  (unless (memq (current-buffer) lazy-lock-buffers)
+    (push (current-buffer) lazy-lock-buffers))
+  ;; A prior deletion that did not cause scrolling, followed by a scroll, would
+  ;; result in an unnecessary trigger after this if we did not cancel it now.
+  (set-window-redisplay-end-trigger window nil))
+
+;; (b) Resizing the window, either explicitly (e.g., `enlarge-window') or
+;;     implicitly (e.g., `delete-other-windows').  Here, `window-end' changes.
+;;     Fontification occurs by adding `lazy-lock-fontify-after-resize' to the
+;;     hook `window-size-change-functions'.
+
+(defun lazy-lock-fontify-after-resize (frame)
+  ;; Called from `window-size-change-functions'.
+  ;; Fontify windows in FRAME following the resize.  We cannot use
+  ;; `window-start' or `window-end' so we fontify conservatively.
+  (save-excursion
+    (save-selected-window
+      (select-frame frame)
+      (walk-windows (function (lambda (window)
+		       (set-buffer (window-buffer window))
+		       (when lazy-lock-mode
+			 (lazy-lock-fontify-conservatively window))
+		       (set-window-redisplay-end-trigger window nil)))
+		    'nomini frame))))
+
+;; (c) Deletion in the buffer.  Here, a `window-end' marker can become visible.
+;;     Fontification occurs by adding `lazy-lock-arrange-before-change' to
+;;     `before-change-functions' and `lazy-lock-fontify-after-trigger' to the
+;;     hook `redisplay-end-trigger-functions'.  Before every deletion, the
+;;     marker `window-redisplay-end-trigger' position is set to the soon-to-be
+;;     changed `window-end' position.  If the marker becomes visible,
+;;     `lazy-lock-fontify-after-trigger' gets called.  Ouch.  Note that we only
+;;     have to deal with this eventuality if there is no on-the-fly deferral.
+
+(defun lazy-lock-arrange-before-change (beg end)
+  ;; Called from `before-change-functions'.
+  ;; Arrange that if text becomes visible it will be fontified (if a deletion
+  ;; is pending, text might become visible at the bottom).
+  (unless (eq beg end)
+    (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)) window)
+      (while windows
+	(setq window (car windows))
+	(unless (markerp (window-redisplay-end-trigger window))
+	  (set-window-redisplay-end-trigger window (make-marker)))
+	(set-marker (window-redisplay-end-trigger window) (window-end window))
+	(setq windows (cdr windows))))))
+
+(defun lazy-lock-fontify-after-trigger (window trigger-point)
+  ;; Called from `redisplay-end-trigger-functions'.
+  ;; Fontify WINDOW from TRIGGER-POINT following the redisplay.
+  ;; We could probably just use `lazy-lock-fontify-after-scroll' without loss:
+  ;;  (inline (lazy-lock-fontify-after-scroll window (window-start window)))
+  (let ((inhibit-point-motion-hooks t))
+    (lazy-lock-fontify-region trigger-point (window-end window t))))
+
+;; 2.  Modified text must be marked as unfontified so it can be identified and
+;;     fontified later when Emacs is idle.  Deferral occurs by adding one of
+;;     `lazy-lock-fontify-*-after-change' (for on-the-fly fontification) or
+;;     `lazy-lock-defer-*-after-change' (for deferred fontification) to the
+;;     hook `after-change-functions'.
+
+(defalias 'lazy-lock-fontify-line-after-change
+  ;; Called from `after-change-functions'.
+  ;; Fontify the current change.
+  'font-lock-after-change-function)
+
+(defun lazy-lock-fontify-rest-after-change (beg end old-len)
+  ;; Called from `after-change-functions'.
+  ;; Fontify the current change and defer fontification of the rest of the
+  ;; buffer.  Save the current buffer so that we subsequently fontify in all
+  ;; windows showing the buffer.
+  (lazy-lock-fontify-line-after-change beg end old-len)
+  (save-buffer-state nil
+    (unless (memq (current-buffer) lazy-lock-buffers)
+      (push (current-buffer) lazy-lock-buffers))
+    (save-restriction
+      (widen)
+      (remove-text-properties end (point-max) '(lazy-lock nil)))))
+
+(defun lazy-lock-defer-line-after-change (beg end old-len)
+  ;; Called from `after-change-functions'.
+  ;; Defer fontification of the current change.  Save the current buffer so
+  ;; that we subsequently fontify in all windows showing the buffer.
+  (save-buffer-state nil
+    (unless (memq (current-buffer) lazy-lock-buffers)
+      (push (current-buffer) lazy-lock-buffers))
+    (remove-text-properties (max (1- beg) (point-min))
+			    (min (1+ end) (point-max))
+			    '(lazy-lock nil))))
+
+(defun lazy-lock-defer-rest-after-change (beg end old-len)
+  ;; Called from `after-change-functions'.
+  ;; Defer fontification of the rest of the buffer.  Save the current buffer so
+  ;; that we subsequently fontify in all windows showing the buffer.
+  (save-buffer-state nil
+    (unless (memq (current-buffer) lazy-lock-buffers)
+      (push (current-buffer) lazy-lock-buffers))
+    (save-restriction
+      (widen)
+      (remove-text-properties (max (1- beg) (point-min))
+			      (point-max)
+			      '(lazy-lock nil)))))
+
+;; 3.  Deferred fontification and stealth fontification are done from these two
+;;     functions.  They are set up as Idle Timers.
+
+(defun lazy-lock-fontify-after-defer ()
+  ;; Called from `timer-idle-list'.
+  ;; Fontify all windows where deferral has occurred for its buffer.
+  (save-excursion
+    (while (and lazy-lock-buffers (not (input-pending-p)))
+      (let ((buffer (car lazy-lock-buffers)) windows)
+	;; Paranoia: check that the buffer is still live and Lazy Lock mode on.
+	(when (buffer-live-p buffer)
+	  (set-buffer buffer)
+	  (when lazy-lock-mode
+	    (setq windows (get-buffer-window-list buffer 'nomini t))
+	    (while windows
+	      (lazy-lock-fontify-window (car windows))
+	      (setq windows (cdr windows)))))
+	(setq lazy-lock-buffers (cdr lazy-lock-buffers)))))
+  ;; Add hook if fontification should now be defer-driven in this buffer.
+  (when (and lazy-lock-mode lazy-lock-defer-on-scrolling
+	     (memq 'lazy-lock-fontify-after-scroll window-scroll-functions)
+	     (not (or (input-pending-p) (lazy-lock-unfontified-p))))
+    (remove-hook 'window-scroll-functions 'lazy-lock-fontify-after-scroll t)
+    (add-hook 'window-scroll-functions 'lazy-lock-defer-after-scroll nil t)))
+
+(defun lazy-lock-fontify-after-idle ()
+  ;; Called from `timer-idle-list'.
+  ;; Fontify all buffers that need it, stealthily while idle.
+  (unless (or executing-kbd-macro (window-minibuffer-p (selected-window)))
+    ;; Loop over all buffers, fontify stealthily for each if necessary.
+    (let ((buffers (buffer-list)) (continue t)
+	  message message-log-max minibuffer-auto-raise)
+      (save-excursion
+	(do-while (and buffers continue)
+	  (set-buffer (car buffers))
+	  (if (not (and lazy-lock-mode (lazy-lock-unfontified-p)))
+	      (setq continue (not (input-pending-p)))
+	    ;; Fontify regions in this buffer while there is no input.
+	    (with-temp-message
+		(when lazy-lock-stealth-verbose
+		  "Fontifying stealthily...")
+	      (do-while (and (lazy-lock-unfontified-p) continue)
+		(if (and lazy-lock-stealth-load
+			 (> (car (load-average)) lazy-lock-stealth-load))
+		    ;; Wait a while before continuing with the loop.
+		    (progn
+		      (when message
+			(message "Fontifying stealthily...suspended")
+			(setq message nil))
+		      (setq continue (sit-for (or lazy-lock-stealth-time 30))))
+		  ;; Fontify a chunk.
+		  (when lazy-lock-stealth-verbose
+		    (if message
+			(message "Fontifying stealthily... %2d%% of %s"
+				 (lazy-lock-percent-fontified) (buffer-name))
+		      (message "Fontifying stealthily...")
+		      (setq message t)))
+		  ;; Current buffer may have changed during `sit-for'.
+		  (set-buffer (car buffers))
+		  (lazy-lock-fontify-chunk)
+		  (setq continue (sit-for (or lazy-lock-stealth-nice 0)))))))
+	  (setq buffers (cdr buffers)))))))
+
+;; 4.  Special circumstances.
+
+(defun lazy-lock-fontify-after-visage ()
+  ;; Called from `outline-view-change-hook' and `hs-hide-hook'.
+  ;; Fontify windows showing the current buffer, as its visibility has changed.
+  ;; This is a conspiracy hack between lazy-lock.el, outline.el and
+  ;; hideshow.el.
+  (let ((windows (get-buffer-window-list (current-buffer) 'nomini t)))
+    (while windows
+      (lazy-lock-fontify-conservatively (car windows))
+      (setq windows (cdr windows)))))
+
+(defun lazy-lock-after-fontify-buffer ()
+  ;; Called from `font-lock-after-fontify-buffer'.
+  ;; Mark the current buffer as fontified.
+  ;; This is a conspiracy hack between lazy-lock.el and font-lock.el.
+  (save-buffer-state nil
+    (add-text-properties (point-min) (point-max) '(lazy-lock t))))
+
+(defun lazy-lock-after-unfontify-buffer ()
+  ;; Called from `font-lock-after-unfontify-buffer'.
+  ;; Mark the current buffer as unfontified.
+  ;; This is a conspiracy hack between lazy-lock.el and font-lock.el.
+  (save-buffer-state nil
+    (remove-text-properties (point-min) (point-max) '(lazy-lock nil))))
+
+;; Fontification functions.
+
+;; If packages want to ensure that some region of the buffer is fontified, they
+;; should use this function.  For an example, see ps-print.el.
+(defun lazy-lock-fontify-region (beg end)
+  ;; Fontify between BEG and END, where necessary, in the current buffer.
+  (save-restriction
+    (widen)
+    (when (setq beg (text-property-any beg end 'lazy-lock nil))
+      (save-excursion
+	(save-match-data
+	  (save-buffer-state
+	   ;; Ensure syntactic fontification is always correct.
+	   (font-lock-beginning-of-syntax-function next)
+	   ;; Find successive unfontified regions between BEG and END.
+	   (condition-case data
+	       (do-while beg
+			 (setq next (or (text-property-any beg end 'lazy-lock t) end))
+	  ;; Make sure the region end points are at beginning of line.
+			 (goto-char beg)
+			 (unless (bolp)
+			   (beginning-of-line)
+			   (setq beg (point)))
+			 (goto-char next)
+			 (unless (bolp)
+			   (forward-line)
+			   (setq next (point)))
+		     ;; Fontify the region, then flag it as fontified.
+			 (font-lock-fontify-region beg next)
+			 (add-text-properties beg next '(lazy-lock t))
+			 (setq beg (text-property-any next end 'lazy-lock nil)))
+	     ((error quit) (message "Fontifying region...%s" data)))))))))
+
+(defun lazy-lock-fontify-chunk ()
+  ;; Fontify the nearest chunk, for stealth, in the current buffer.
+  (let ((inhibit-point-motion-hooks t))
+    (save-excursion
+      (save-restriction
+	(widen)
+	;; Move to end of line in case the character at point is not fontified.
+	(end-of-line)
+	;; Find where the previous (next) unfontified regions end (begin).
+	(let ((prev (previous-single-property-change (point) 'lazy-lock))
+	      (next (text-property-any (point) (point-max) 'lazy-lock nil)))
+	  ;; Fontify from the nearest unfontified position.
+	  (if (or (null prev) (and next (< (- next (point)) (- (point) prev))))
+	      ;; The next, or neither, region is the nearest not fontified.
+	      (lazy-lock-fontify-region
+	       (progn (goto-char (or next (point-min)))
+		      (beginning-of-line)
+		      (point))
+	       (progn (goto-char (or next (point-min)))
+		      (forward-line lazy-lock-stealth-lines)
+		      (point)))
+	    ;; The previous region is the nearest not fontified.
+	    (lazy-lock-fontify-region
+	     (progn (goto-char prev)
+		    (forward-line (- lazy-lock-stealth-lines))
+		    (point))
+	     (progn (goto-char prev)
+		    (forward-line)
+		    (point)))))))))
+
+(defun lazy-lock-fontify-window (window)
+  ;; Fontify in WINDOW between `window-start' and `window-end'.
+  ;; We can only do this when we can use `window-start' and `window-end'.
+  (with-current-buffer (window-buffer window)
+    (lazy-lock-fontify-region (window-start window) (window-end window))))
+
+(defun lazy-lock-fontify-conservatively (window)
+  ;; Fontify in WINDOW conservatively around point.
+  ;; Where we cannot use `window-start' and `window-end' we do `window-height'
+  ;; lines around point.  That way we guarantee to have done enough.
+  (with-current-buffer (window-buffer window)
+    (let ((inhibit-point-motion-hooks t))
+      (lazy-lock-fontify-region
+       (save-excursion
+	 (goto-char (window-point window))
+	 (vertical-motion (- (window-height window)) window) (point))
+       (save-excursion
+	 (goto-char (window-point window))
+	 (vertical-motion (window-height window) window) (point))))))
+
+(defun lazy-lock-unfontified-p ()
+  ;; Return non-nil if there is anywhere still to be fontified.
+  (save-restriction
+    (widen)
+    (text-property-any (point-min) (point-max) 'lazy-lock nil)))
+
+(defun lazy-lock-percent-fontified ()
+  ;; Return the percentage (of characters) of the buffer that are fontified.
+  (save-restriction
+    (widen)
+    (let ((beg (point-min)) (size 0) next)
+      ;; Find where the next fontified region begins.
+      (while (setq beg (text-property-any beg (point-max) 'lazy-lock t))
+	(setq next (or (text-property-any beg (point-max) 'lazy-lock nil)
+		       (point-max)))
+	(incf size (- next beg))
+	(setq beg next))
+      ;; Float because using integer multiplication will frequently overflow.
+      (truncate (* (/ (float size) (point-max)) 100)))))
+
+;; Version dependent workarounds and fixes.
+
+(when (consp lazy-lock-defer-time)
+  ;;
+  ;; In 2.06.04 and below, `lazy-lock-defer-time' could specify modes and time.
+  (with-output-to-temp-buffer "*Help*"
+    (princ "The value of the variable `lazy-lock-defer-time' was\n ")
+    (princ lazy-lock-defer-time)
+    (princ "\n")
+    (princ "This variable cannot now be a list of modes and time,\n")
+    (princ "so instead use ")
+    (princ (substitute-command-keys "\\[customize-option]"))
+    (princ " to modify the variables, or put the forms:\n")
+    (princ " (setq lazy-lock-defer-time ")
+    (princ (cdr lazy-lock-defer-time))
+    (princ ")\n")
+    (princ " (setq lazy-lock-defer-on-the-fly '")
+    (princ (car lazy-lock-defer-time))
+    (princ ")\n")
+    (princ "in your ~/.emacs.  ")
+    (princ "The above forms have been evaluated for this editor session,\n")
+    (princ "but you should use ")
+    (princ (substitute-command-keys "\\[customize-option]"))
+    (princ " or change your ~/.emacs now."))
+  (setq lazy-lock-defer-on-the-fly (car lazy-lock-defer-time)
+	lazy-lock-defer-time (cdr lazy-lock-defer-time)))
+
+(when (boundp 'lazy-lock-defer-driven)
+  ;;
+  ;; In 2.06.04 and below, `lazy-lock-defer-driven' was the variable name.
+  (with-output-to-temp-buffer "*Help*"
+    (princ "The value of the variable `lazy-lock-defer-driven' is set to ")
+    (if (memq lazy-lock-defer-driven '(nil t))
+	(princ lazy-lock-defer-driven)
+      (princ "`")
+      (princ lazy-lock-defer-driven)
+      (princ "'"))
+    (princ ".\n")
+    (princ "This variable is now called `lazy-lock-defer-on-scrolling',\n")
+    (princ "so instead use ")
+    (princ (substitute-command-keys "\\[customize-option]"))
+    (princ " to modify the variable, or put the form:\n")
+    (princ " (setq lazy-lock-defer-on-scrolling ")
+    (unless (memq lazy-lock-defer-driven '(nil t))
+      (princ "'"))
+    (princ lazy-lock-defer-driven)
+    (princ ")\n")
+    (princ "in your ~/.emacs.  ")
+    (princ "The above form has been evaluated for this editor session,\n")
+    (princ "but you should use ")
+    (princ (substitute-command-keys "\\[customize-option]"))
+    (princ " or change your ~/.emacs now."))
+  (setq lazy-lock-defer-on-scrolling lazy-lock-defer-driven))
+
+;; Install ourselves:
+
+(add-hook 'window-size-change-functions 'lazy-lock-fontify-after-resize)
+(add-hook 'redisplay-end-trigger-functions 'lazy-lock-fontify-after-trigger)
+
+(unless (assq 'lazy-lock-mode minor-mode-alist)
+  (setq minor-mode-alist (append minor-mode-alist '((lazy-lock-mode nil)))))
+
+;; Provide ourselves:
+
+(provide 'lazy-lock)
+
+;;; arch-tag: c1776846-f046-4a45-9684-54b951b12fc9
+;;; lazy-lock.el ends here