[nongnu] elpa/devhelp 2e257e2d12 01/13: Add devhelp.el, README.org and COPYING

[ELPA Syncer]

branch: elpa/devhelp
commit 2e257e2d1271d88f09fd09661ba4b705febc1b3c
Author: Akib Azmain Turja <akib@disroot.org>
Commit: Akib Azmain Turja <akib@disroot.org>

    Add devhelp.el, README.org and COPYING
---
 COPYING    | 674 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 README.org |  48 +++++
 devhelp.el | 597 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 1319 insertions(+)

diff --git a/COPYING b/COPYING
new file mode 100644
index 0000000000..f288702d2f
--- /dev/null
+++ b/COPYING
@@ -0,0 +1,674 @@
+                    GNU GENERAL PUBLIC LICENSE
+                       Version 3, 29 June 2007
+
+ Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
+ Everyone is permitted to copy and distribute verbatim copies
+ of this license document, but changing it is not allowed.
+
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+APPLICABLE LAW.  EXCEPT WHEN OTHERWISE STATED IN WRITING THE COPYRIGHT
+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE.  THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU.  SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+  16. Limitation of Liability.
+
+  IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+  17. Interpretation of Sections 15 and 16.
+
+  If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+                     END OF TERMS AND CONDITIONS
+
+            How to Apply These Terms to Your New Programs
+
+  If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+  To do so, attach the following notices to the program.  It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+    <one line to give the program's name and a brief idea of what it does.>
+    Copyright (C) <year>  <name of author>
+
+    This program 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 3 of the License, or
+    (at your option) any later version.
+
+    This program 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 this program.  If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+  If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+    <program>  Copyright (C) <year>  <name of author>
+    This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+    This is free software, and you are welcome to redistribute it
+    under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License.  Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+  You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+  The GNU General Public License does not permit incorporating your program
+into proprietary programs.  If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library.  If this is what you want to do, use the GNU Lesser General
+Public License instead of this License.  But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/README.org b/README.org
new file mode 100644
index 0000000000..b27390c52c
--- /dev/null
+++ b/README.org
@@ -0,0 +1,48 @@
+#+title: Devhelp - Browse documentation in Devhelp format
+
+In this unfortunate world, many documentations are using various HTML based
+format, instead of using the excellent Texinfo and Info format.  This makes
+integrating of these manuals with Emacs hard, although not impossible.
+
+This package make tries to integrate one of those stupid formats, Devhelp,
+with Emacs.
+
+* Usage
+
+=M-x devhelp= and you are good to go.  But you use a system that isn't FHS
+(Filesystem Hierarchy Standard) compliant, then you would need to change
+it.  For example, you have to put the following in the init file for GNU
+Guix:
+
+#+begin_src emacs-lisp
+(setq devhelp-search-directories
+      '("/run/current-system/profile/share/doc/"
+        "/run/current-system/profile/share/gtk-doc/html/"
+        "~/.guix-profile/share/doc/"
+        "~/.guix-profile/share/gtk-doc/html/"))
+#+end_src
+
+You can also bookmark pages, with the standard ~bookmark-set~ function.
+
+* Installation
+
+Devhelp isn't available on any ELPA right now.  So, you have to follow one
+of the following methods:
+
+** Quelpa
+
+#+begin_src emacs-lisp
+(quelpa '(devhelp :fetcher git
+                  :url "https://codeberg.org/akib/emacs-devhelp.git";))
+#+end_src
+
+** Straight.el
+
+#+begin_src emacs-lisp
+(straight-use-package
+ '(devhelp :type git :repo "https://codeberg.org/akib/emacs-devhelp.git";))
+#+end_src
+
+** Manual
+
+Download the ~devhelp.el~ file and put it in your ~load-path~.
diff --git a/devhelp.el b/devhelp.el
new file mode 100644
index 0000000000..18433eb97c
--- /dev/null
+++ b/devhelp.el
@@ -0,0 +1,597 @@
+;;; devhelp.el --- Browse documentation in Devhelp format  -*- 
lexical-binding: t; -*-
+
+;; Copyright (C) 2022 Akib Azmain Turja.
+
+;; Author: Akib Azmain Turja <akib@disroot.org>
+;; Created: 2022-07-26
+;; Version: 0.1
+;; Package-Requires: ((emacs "27.1"))
+;; Keywords: convenience
+;; URL: https://codeberg.org/akib/emacs-devhelp
+
+;; This file is not part of GNU Emacs.
+
+;; This file 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 3, or (at your option)
+;; any later version.
+
+;; This program 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.
+
+;; For a full copy of the GNU General Public License
+;; see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; In this unfortunate world, many documentations are using various HTML
+;; based format, instead of using the excellent Texinfo and Info format.
+;; This makes integrating of these manuals with Emacs hard, although not
+;; impossible.
+
+;; This package make tries to integrate one of those stupid formats,
+;; Devhelp, with Emacs.
+
+;; Usage
+;; -----
+
+;; M-x devhelp and you are good to go.  But you use a system that isn't FHS
+;; (Filesystem Hierarchy Standard) compliant, then you would need to change
+;; it.  For example, you have to put the following in the init file for GNU
+;; Guix:
+
+;;     (setq devhelp-search-directories
+;;           '("/run/current-system/profile/share/doc/"
+;;             "/run/current-system/profile/share/gtk-doc/html/"
+;;             "~/.guix-profile/share/doc/"
+;;             "~/.guix-profile/share/gtk-doc/html/"))
+
+;; You can also bookmark pages, with the standard `bookmark-set' function.
+
+;;; Code:
+
+(eval-when-compile (require 'cl-lib))
+(require 'dom)
+(require 'shr)
+(require 'bookmark)
+
+(defgroup devhelp nil
+  "Browse documentation in Devhelp format."
+  :group 'convenience
+  :link '(url-link "https://codeberg.org/akib/emacs-devhelp";)
+  :prefix "devhelp-")
+
+(defcustom devhelp-use-variable-pitch-font t
+  "Non-nil means use variable pitch (proportional) font."
+  :type 'boolean)
+
+(defcustom devhelp-text-width nil
+  "Window width to use for HTML rendering.
+
+Integer means use that many columns.  Nil means use full window width."
+  :type '(choice (integer :tag "Fixed width in characters")
+                (const :tag "Use the width of the window" nil)))
+
+(defcustom devhelp-toc-group-books-by-language t
+  "Non-nil means group books by language in table of contents."
+  :type 'boolean)
+
+(defcustom devhelp-index-group-keywords-by-type t
+  "Non-nil means group keywords by type in index."
+  :type 'boolean)
+
+(defcustom devhelp-search-directories
+  '("/usr/share/doc/" "/usr/share/gtk-doc/html/" "/usr/local/share/doc/"
+    "/usr/local/share/gtk-doc/html/")
+  "List of directories to search for Devhelp books.
+
+Note that on GNU Guix, Nix or other FHS (Filesystem Hierarchy Standard)
+non-compliant distributions, the default value won't work.  For GNU Guix,
+set it to '(\"/run/current-system/profile/share/doc/\"
+\"/run/current-system/profile/share/gtk-doc/html/\"
+\"~/.guix-profile/share/doc/\" \"~/.guix-profile/share/gtk-doc/html/\")."
+  :type '(repeat directory))
+
+(defvar devhelp--books nil
+  "Necessary data extracted from Devhelp file.
+
+Each element is a list returned by `devhelp--parse-devhelp-file'.")
+
+(defvar devhelp--history nil
+  "History of pages visited by the user.
+
+The value is of form (CURRENT . STACK), where STACK is the stack of user
+visited pages, and CURRENT is the index of current page in STACK.  Each
+element of STACK is a list of form (TITLE FILE BUFFERPOS), where TITLE is
+the title of the page, FILE is the FILE name followed by optional target
+\(see `url-generic-parse-url') and BUFFERPOS is the position in buffer.
+FILE can also be the symbol `toc', meaning the table of contents page.")
+
+(defun devhelp--parse-devhelp-file (file)
+  "Parse Devhelp file FILE and return book data.
+
+Return a list of form (TITLE NAME LANGUAGE PATH CHAPTERS KEYWORDS), where
+TITLE is the title of book, NAME is the name of the book, LANGUAGE is the
+ programming language name, PATH is the absolute path to it, CHAPTER is a
+list of form (SECTION...) and KEYWORDS is a list of form (KEYWORD...).
+SECTION is a list of form (NAME PATH SUB-SECTIONS...), where NAME is the
+name of the section, PATH is the absolute path to the file and SUB-SECTION
+is a list of form (SECTION...).  KEYWORD is a list of (NAME TYPE PATH),
+where NAME  the keyword name, TYPE is the type of keyword and PATH is the
+absolute path to it."
+  (unless (fboundp 'libxml-parse-html-region)
+    (error "This function requires Emacs to be compiled with libxml2"))
+  (let* ((dom (with-temp-buffer
+                (insert-file-contents file)
+                (libxml-parse-xml-region (point-min) (point-max))))
+         (version (pcase (if (string= (file-name-extension file) "gz")
+                             (file-name-extension
+                              (file-name-sans-extension file))
+                           (file-name-extension file))
+                    ("devhelp" 1)
+                    ("devhelp2" 2)
+                    (_ (error "Invalid Devhelp file"))))
+         (base (expand-file-name (or (dom-attr dom 'base) "")
+                                 (file-name-directory file))))
+    (cl-labels ((children-by-tag
+                 (tree tag)
+                 (mapcan (lambda (node)
+                           (when (and (listp node) (eq (dom-tag node) tag))
+                             (list node)))
+                         (dom-children tree)))
+                (process-section
+                 (sec)
+                 `(,(dom-attr sec 'name)
+                   ,(expand-file-name (dom-attr sec 'link) base)
+                   ,(mapcar #'process-section (children-by-tag
+                                               sec 'sub)))))
+      `(,(or (dom-attr dom 'title) "Untitled")
+        ,(or (dom-attr dom 'name) (file-name-base file))
+        ,(or (dom-attr dom 'language) "any")
+        ,(expand-file-name (dom-attr dom 'link) base)
+        ,(mapcar #'process-section
+                 (mapcan (lambda (tree) (children-by-tag tree 'sub))
+                         (children-by-tag dom 'chapters)))
+        ,(mapcar
+          (lambda (kw)
+            `(,(dom-attr kw 'name)
+              ,(or (dom-attr kw 'type) "function")
+              ,(expand-file-name (dom-attr kw 'link) base)))
+          (mapcan (lambda (tree)
+                    (children-by-tag
+                     tree (if (eq version 1) 'function 'keyword)))
+                  (children-by-tag dom 'functions)))))))
+
+(defun devhelp--search-for-books ()
+  "Search for Devhelp books in `devhelp-search-directories'.
+
+Return a list of book data returned by `devhelp--parse-devhelp-file' for
+each valid Devhelp books."
+  (unless (fboundp 'libxml-parse-html-region)
+    (error "This function requires Emacs to be compiled with libxml2"))
+  (let ((books nil))
+    (dolist (path devhelp-search-directories)
+      (when (file-directory-p path)
+        (dolist (dir (directory-files path))
+          (when (and (file-directory-p (expand-file-name dir path))
+                     (not (member dir '("." ".."))))
+            (catch 'stop
+              (dolist (suffix '(".devhelp2" ".devhelp2.gz"
+                                ".devhelp" ".devhelp.gz"))
+                (let ((file (expand-file-name
+                             (concat dir suffix)
+                             (expand-file-name dir path))))
+                  (when (file-regular-p file)
+                    (ignore-errors
+                      (push (devhelp--parse-devhelp-file file) books)
+                      (throw 'stop nil))))))))))
+    (sort books (lambda (a b) (string< (car a) (car b))))))
+
+(defun devhelp--file-to-url (file)
+  "Convert path FILE to URL and return it."
+  (concat "file://" (and (memq system-type '(windows-nt ms-dos)) "/")
+          file))
+
+(defun devhelp-toc ()
+  "Open table of contents, of all books.
+
+If a single file was opened, only show that book's table of contents."
+  (interactive)
+  (when (cdr devhelp--history)
+    (if (eq (nth 1 (nth (car devhelp--history) (cdr devhelp--history)))
+            'history)
+        (setf (nthcdr (car devhelp--history) (cdr devhelp--history))
+              (nthcdr (1+ (car devhelp--history)) (cdr devhelp--history)))
+      (setf (nth 2 (nth (car devhelp--history) (cdr devhelp--history)))
+            (point))
+      (setf (cdr devhelp--history) (nthcdr (car devhelp--history)
+                                           (cdr devhelp--history)))))
+  (setf (car devhelp--history) 0)
+  (push (list nil 'toc (point-min)) (cdr devhelp--history))
+  (devhelp--toc-1)
+  (goto-char (point-min)))
+
+(defun devhelp--toc-1 ()
+  "Show table of contents.
+
+See `devhelp-toc' for more details."
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert
+     "<html><head><title>Table of contents</title></head><body><ul>"
+     (let ((book-tocs
+            (mapcar
+             (lambda (book)
+               (cl-labels ((section-to-html
+                            (section)
+                            (concat
+                             "<li>"
+                             (format
+                              "<a href=%S>%s</a>"
+                              (devhelp--file-to-url (nth 1 section))
+                              (nth 0 section))
+                             (when (nth 2 section)
+                               (format
+                                "<ul>%s</ul>"
+                                (mapconcat #'section-to-html
+                                           (nth 2 section) "")))
+                             "</li>")))
+                 (cons
+                  (nth 2 book)
+                  (concat
+                   (format
+                    "<b><a href=%S>%s</a></b>"
+                    (devhelp--file-to-url (nth 3 book)) (nth 0 book))
+                   (when (nth 4 book)
+                     (format
+                      "<ul>%s</ul>"
+                      (mapconcat #'section-to-html (nth 4 book) "")))))))
+             devhelp--books)))
+       (if (not devhelp-toc-group-books-by-language)
+           (mapconcat (lambda (toc) (format "<li>%s</li>" (cdr toc)))
+                      book-tocs "")
+         (let ((groups nil))
+           (dolist (toc book-tocs)
+             (if-let ((pair (assoc (car toc) groups)))
+                 (setf (cdr pair) (nconc (cdr pair) (list (cdr toc))))
+               (push (cons (car toc) (list (cdr toc))) groups)))
+           (setq groups (sort groups (lambda (a b)
+                                       (string< (car a) (car b)))))
+           (mapconcat
+            (lambda (group)
+              (when (cdr group)
+                (format
+                 "<li><b><u>Language: %s</u></b><ul>%s</ul></li>"
+                 (capitalize (car group))
+                 (mapconcat (lambda (toc) (format "<li>%s</li>" toc))
+                            (cdr group) ""))))
+            groups ""))))
+     "</ul></body></html>")
+    (devhelp--render-html)
+    (goto-char (point-min))))
+
+(defun devhelp-index ()
+  "Show index, of all books.
+
+If a single file was opened, only show that book's index."
+  (interactive)
+  (when (cdr devhelp--history)
+    (if (eq (nth 1 (nth (car devhelp--history) (cdr devhelp--history)))
+            'history)
+        (setf (nthcdr (car devhelp--history) (cdr devhelp--history))
+              (nthcdr (1+ (car devhelp--history)) (cdr devhelp--history)))
+      (setf (nth 2 (nth (car devhelp--history) (cdr devhelp--history)))
+            (point))
+      (setf (cdr devhelp--history) (nthcdr (car devhelp--history)
+                                           (cdr devhelp--history)))))
+  (setf (car devhelp--history) 0)
+  (push (list nil 'index (point-min)) (cdr devhelp--history))
+  (devhelp--index-1)
+  (goto-char (point-min)))
+
+(defun devhelp--index-1 ()
+  "Show table of contents.
+
+See `devhelp-index' for more details."
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert
+     "<html><head><title>Index</title></head><body><ul>"
+     (let ((keywords (mapcan (lambda (book)
+                            (copy-sequence (nth 5 book)))
+                          devhelp--books)))
+       (sort keywords (lambda (a b) (string< (car a) (car b))))
+       (if (not devhelp-index-group-keywords-by-type)
+           (mapconcat (lambda (keyword)
+                        (format "<li>%s <a href=%S>%s</a></li>"
+                                (capitalize (nth 1 keyword))
+                                (devhelp--file-to-url (nth 2 keyword))
+                                (nth 0 keyword)))
+                      keywords "")
+         (let ((groups nil))
+           (dolist (keyword keywords)
+             (let ((entry (format "<a href=%S>%s</a>"
+                                  (devhelp--file-to-url (nth 2 keyword))
+                                  (nth 0 keyword))))
+               (if-let ((pair (assoc (nth 1 keyword) groups)))
+                   (setf (cdr pair) (nconc (cdr pair) (list entry)))
+                 (push (cons (nth 1 keyword) (list entry)) groups))))
+           (setq groups (sort groups (lambda (a b)
+                                       (string< (car a) (car b)))))
+           (mapconcat
+            (lambda (group)
+              (when (cdr group)
+                (format
+                 "<li><b><u>Type: %s</u></b><ul>%s</ul></li>"
+                 (capitalize (car group))
+                 (mapconcat (lambda (entry) (format "<li>%s</li>" entry))
+                            (cdr group) ""))))
+            groups ""))))
+     "</ul></body></html>")
+    (devhelp--render-html)
+    (goto-char (point-min))))
+
+(defun devhelp--set-title (title)
+  "Set the title of current page to TITLE."
+  (setq header-line-format
+        (when title (replace-regexp-in-string "%" "%%" title)))
+  (setf (car (nth (car devhelp--history) (cdr devhelp--history))) title))
+
+(defun devhelp-browse-url (&optional event)
+  "Follow link under point/mouse.
+
+EVENT is a mouse event, if any."
+  (interactive (list last-nonmenu-event))
+  (mouse-set-point event)
+  (let ((link (get-text-property (point) 'shr-url)))
+    (devhelp--browse-url-1 link)))
+
+(defun devhelp--browse-url-1 (link)
+  "Goto url specified in LINK."
+  (if (not (stringp link))
+      (user-error "No link under point")
+    (if-let ((url (url-generic-parse-url link))
+             ((string= (url-type url) "file"))
+             (file (url-filename url)))
+        (progn
+          (when (cdr devhelp--history)
+            (setf (nth 2 (nth (car devhelp--history)
+                              (cdr devhelp--history)))
+                  (point))
+            (setf (cdr devhelp--history)
+                  (nthcdr (car devhelp--history)
+                          (cdr devhelp--history))))
+          (setf (car devhelp--history) 0)
+          (push (list nil (url-recreate-url (url-parse-make-urlobj
+                                             nil nil nil nil nil file
+                                             (url-target url)))
+                      (point-min))
+                (cdr devhelp--history))
+          (devhelp--set-title "Untitled")
+          (devhelp--render-html-file
+           (if (memq system-type '(windows-nt ms-dos))
+               (substring file 1)
+             file))
+          (goto-char (point-min))
+          (when (and (url-target url)
+                     (not (string-empty-p (url-target url))))
+            (text-property-search-forward 'shr-target-id (url-target url)))
+          (recenter 0)
+          (setf (nth 2 (nth 0 (cdr devhelp--history))) (point)))
+      (browse-url url))))
+
+(defun devhelp--render-html (&optional base)
+  "Render HTML in current buffer.
+
+When BASE is given, use it to make relative URLs absolute."
+  (let ((shr-map
+         (let ((map (make-sparse-keymap)))
+           (set-keymap-parent map shr-map)
+           (let ((fn (if (eq (nth 1 (nth (car devhelp--history)
+                                         (cdr devhelp--history)))
+                             'history)
+                         #'devhelp-history-goto #'devhelp-browse-url)))
+             (define-key map (kbd "RET") fn)
+             (define-key map [mouse-2] fn))
+           map))
+        (shr-external-rendering-functions
+         (append `((title
+                    . ,(lambda (dom)
+                         (devhelp--set-title (car (dom-children dom))))))
+                 shr-external-rendering-functions))
+        (shr-use-fonts devhelp-use-variable-pitch-font)
+        (shr-width devhelp-text-width)
+        (dom (libxml-parse-html-region (point-min) (point-max))))
+    (erase-buffer)
+    (shr-insert-document (if base `(base ((href . ,base)) (,dom)) dom))
+    (goto-char (point-min))))
+
+(defun devhelp--render-html-file (file)
+  "Load and render HTML file FILE in current buffer."
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert-file-contents file)
+    (devhelp--render-html (devhelp--file-to-url file))))
+
+(defun devhelp--history-goto (n)
+  "Goto Nth page in `devhelp--history'."
+  (if (not (< -1 n (if (eq (nth 1 (nth (car devhelp--history)
+                                       (cdr devhelp--history)))
+                           'history)
+                       (1- (length (cdr devhelp--history)))
+                     (length (cdr devhelp--history)))))
+      (user-error (concat (if (< n 0) "Beginning" "End") " of history"))
+    (when (eq (nth 1 (nth (car devhelp--history) (cdr devhelp--history)))
+              'history)
+      (setf (nthcdr (car devhelp--history) (cdr devhelp--history))
+            (nthcdr (1+ (car devhelp--history)) (cdr devhelp--history))))
+    (setf (nth 2 (nth (car devhelp--history)
+                      (cdr devhelp--history)))
+          (point))
+    (setf (car devhelp--history) n)
+    (if (symbolp (nth 1 (nth n (cdr devhelp--history))))
+        (pcase (nth 1 (nth n (cdr devhelp--history)))
+          ('toc (devhelp--toc-1))
+          ('index (devhelp--index-1)))
+      (let* ((url (url-generic-parse-url
+                   (devhelp--file-to-url
+                    (nth 1 (nth n (cdr devhelp--history))))))
+             (file (url-filename url)))
+        (devhelp--render-html-file
+         (if (memq system-type '(windows-nt ms-dos))
+             (substring file 1)
+           file))))
+    (goto-char (nth 2 (nth n (cdr devhelp--history))))
+    (recenter)))
+
+(defun devhelp-history-back (&optional n)
+  "Go to the previous page.
+
+When prefix argument N is given, go to Nth previous page."
+  (interactive "p")
+  (devhelp--history-goto (+ (car devhelp--history) n)))
+
+(defun devhelp-history-forward (&optional n)
+  "Go to the next page.
+
+When prefix argument N is given, go to Nth next page."
+  (interactive "p")
+  (devhelp--history-goto (- (car devhelp--history) n)))
+
+(defun devhelp-history-goto (&optional event)
+  "Go to history link under point.
+
+This only works in history page.
+
+EVENT is a mouse event, if any."
+  (interactive (list last-nonmenu-event))
+  (mouse-set-point event)
+  (unless (eq (nth 1 (nth (car devhelp--history)
+                          (cdr devhelp--history)))
+              'history)
+    (user-error "Not in history page"))
+  (devhelp--history-goto
+   (string-to-number (get-text-property (point) 'shr-url))))
+
+(defun devhelp-history ()
+  "Show history."
+  (interactive)
+  (setf (nth 2 (nth (car devhelp--history) (cdr devhelp--history)))
+        (point))
+  (let ((inhibit-read-only t))
+    (erase-buffer)
+    (insert "<html><head><title>History of visited pages</title></head>"
+            "<body><h1>History of visited pages</h1><ul>")
+    (dolist (i (number-sequence 0 (1- (length (cdr devhelp--history)))))
+      (insert (format "<li><a href=\"%i\">%s</a></li>" i
+                      (let ((title (car (nth i (cdr devhelp--history)))))
+                        (if (eq i (car devhelp--history))
+                            (format "<i>%s</i>" title)
+                          title)))))
+    (insert "</ul></body></html>")
+    (push (list nil 'history (point-min)) (nthcdr (car devhelp--history)
+                                                  (cdr devhelp--history)))
+    (devhelp--render-html)))
+
+(defun devhelp--directory ()
+  "List all available Devhelp books."
+  (message "Composing Devhelp directory...")
+  (setq devhelp--books (devhelp--search-for-books))
+  (devhelp-toc)
+  (message "Composing Devhelp directory...done"))
+
+(defun devhelp--open-file (file)
+  "Open FILE in current buffer."
+  (setq devhelp--books (list (devhelp--parse-devhelp-file file)))
+  (devhelp--browse-url-1 (devhelp--file-to-url
+                          (nth 3 (car devhelp--books)))))
+
+;;;###autoload
+(defun devhelp (file buffer)
+  "Browse documentation in Devhelp format.
+
+Interactively, when a non-numeric prefix argument is given, the Devhelp
+file name is read interactively from the minibuffer.  When a numeric
+argument N is given, a buffer named \"*devhelp*<N>\" is selected.
+
+Optional argument BUFFER specifies the BUFFER to use, it can be a live
+buffer or a buffer name.  If BUFFER is a buffer name and the buffer doesn't
+exist, it is created.
+
+Optional argument FILE specifies the file to open, the default is to open
+the conbined table of contents of all available Devhelp books."
+  (interactive
+   (list (when (and current-prefix-arg (not (numberp current-prefix-arg)))
+           (read-file-name "Devhelp file name: " nil nil t))
+         (when (numberp current-prefix-arg)
+           (format "*devhelp*<%s>" current-prefix-arg))))
+  (unless (fboundp 'libxml-parse-html-region)
+    (error "This function requires Emacs to be compiled with libxml2"))
+  (with-current-buffer (get-buffer-create (or buffer "*devhelp*"))
+    (devhelp-mode)
+    (display-buffer (current-buffer))
+    (if (not file)
+        (devhelp--directory)
+      (devhelp--open-file file))))
+
+(defun devhelp--make-bookmark-record ()
+  "Make a bookmark record."
+  (let ((entry (nth (car devhelp--history) (cdr devhelp--history))))
+    `(,(nth 0 entry)
+      (filename . ,(when (stringp (nth 1 entry)) (nth 1 entry)))
+      (file . ,(nth 1 entry))
+      (position . ,(nth 2 entry))
+      (handler . devhelp-bookmake-jump))))
+
+;;;###autoload
+(defun devhelp-bookmake-jump (bookmark)
+  "Jump to BOOKMARK."
+  (unless (fboundp 'libxml-parse-html-region)
+    (error "This function requires Emacs to be compiled with libxml2"))
+  (with-current-buffer (generate-new-buffer "*devhelp*")
+    (devhelp-mode)
+    (display-buffer (current-buffer))
+    (setq devhelp--books (devhelp--search-for-books))
+    (setq devhelp--history
+          `(0 . ((nil ,(bookmark-prop-get bookmark 'file)
+                      ,(bookmark-prop-get bookmark 'position)))))
+    (if (symbolp (bookmark-prop-get bookmark 'file))
+        (pcase (bookmark-prop-get bookmark 'file)
+          ('toc (devhelp--toc-1))
+          ('index (devhelp--index-1)))
+      (let ((file (url-filename
+                   (url-generic-parse-url
+                    (devhelp--file-to-url
+                     (bookmark-prop-get bookmark 'file))))))
+        (devhelp--set-title "Untitled")
+        (devhelp--render-html-file
+         (if (memq system-type '(windows-nt ms-dos))
+             (substring file 1)
+           file))
+        (goto-char (min (max (bookmark-prop-get bookmark 'position)
+                             (point-min))
+                        (point-max)))
+        (recenter 0)
+        (setf (nth 2 (nth 0 (cdr devhelp--history))) (point))))))
+
+(defvar devhelp-mode-map
+  (let ((map (make-sparse-keymap)))
+    (define-key map (kbd "i") #'devhelp-index)
+    (define-key map (kbd "d") #'devhelp-toc)
+    (define-key map (kbd "l") #'devhelp-history-back)
+    (define-key map (kbd "r") #'devhelp-history-forward)
+    (define-key map (kbd "L") #'devhelp-history)
+    map)
+  "Keymap for Devhelp mode.")
+
+(define-derived-mode devhelp-mode special-mode "Devhelp"
+  "Major mode for browsing Devhelp books."
+  (setq-local devhelp--books nil)
+  (setq-local devhelp--history '(nil . nil))
+  (setq-local bookmark-make-record-function
+              #'devhelp--make-bookmark-record))
+
+(provide 'devhelp)
+;;; devhelp.el ends here