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+;;; org-e-beamer.el --- Beamer Back-End for Org Export Engine
+
+;; Copyright (C) 2007-2012  Free Software Foundation, Inc.
+
+;; Author: Carsten Dominik <carsten.dominik AT gmail DOT com>
+;;         Nicolas Goaziou <n.goaziou AT gmail DOT com>
+;; Keywords: org, wp, tex
+
+;; 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 3 of the License, 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.  If not, see <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; This library implements both a Beamer back-end, derived from the
+;; LaTeX one and a minor mode easing structure edition of the
+;; document.
+;;
+;; Depending on the desired output format, three commands are provided
+;; for export: `org-e-beamer-export-as-latex' (temporary buffer),
+;; `org-e-beamer-export-to-latex' ("tex" file) and
+;; `org-e-beamer-export-to-pdf' ("pdf" file).
+;;
+;; On top of buffer keywords supported by `e-latex' back-end (see
+;; `org-e-latex-options-alist'), this back-end introduces the
+;; following keywords: "BEAMER_THEME", "BEAMER_COLOR_THEME",
+;; "BEAMER_FONT_THEME", "BEAMER_INNER_THEME" and "BEAMER_OUTER_THEME".
+;; All accept options in square brackets.
+;;
+;; Moreover, headlines now fall into three categories: sectioning
+;; elements, frames and blocks.
+;;
+;; - Like `e-latex' back-end sectioning elements are still set through
+;;   `org-e-latex-classes' variable.
+;;
+;; - Headlines become frames when their level is equal to
+;;   `org-e-beamer-frame-level' (or "H" value in the OPTIONS line).
+;;   Though, if an headline in the current tree has a "BEAMER_env"
+;;   (see below) property set to "frame", its level overrides the
+;;   variable.
+;;
+;; - All frames' children become block environments.  Special block
+;;   types can be enforced by setting headline's "BEAMER_env" property
+;;   to an appropriate value (see `org-e-beamer-environments-default'
+;;   for supported value and `org-e-beamer-environments-extra' for
+;;   adding more).
+;;
+;; - As a special case, if the "BEAMER_env" property is set to either
+;;   "appendix", "note" or "noteNH", the headline will become,
+;;   respectively, an appendix, a note (within frame or between frame,
+;;   depending on its level) and a note with its title ignored.
+;;
+;;   Also, an headline with an "ignoreheading" value will have its
+;;   contents only inserted in the output.  This special value is
+;;   useful to have data between frames, or to properly close
+;;   a "column" environment.
+;;
+;; Along with "BEAMER_env", headlines also support "BEAMER_act" and
+;; "BEAMER_opt" properties.  The former is translated as an
+;; overlay/action specification (or a default overlay specification
+;; when enclosed within square brackets) whereas the latter specifies
+;; options for the current frame ("fragile" option is added
+;; automatically, though).
+;;
+;; Every plain list has support for `:overlay' attribute (through
+;; ATTR_BEAMER affiliated keyword).  Also, ordered (resp. description)
+;; lists make use of `:template' (resp. `:long-text') attribute.
+;;
+;; Eventually, an export snippet with a value enclosed within angular
+;; brackets put at the beginning of an element or object whose type is
+;; among `bold', `item', `link', `radio-target' and `target' will
+;; control its overlay specifications.
+;;
+;; On the minor mode side, `org-e-beamer-select-environment' (bound by
+;; default to "C-c C-b") and `org-e-beamer-insert-options-template'
+;; are the two entry points.
+
+;;; Code:
+
+(require 'org-e-latex)
+
+
+
+;;; User-Configurable Variables
+
+(defgroup org-export-e-beamer nil
+  "Options specific for using the beamer class in LaTeX export."
+  :tag "Org Beamer"
+  :group 'org-export
+  :version "24.2")
+
+(defcustom org-e-beamer-frame-level 1
+  "The level at which headlines become frames.
+
+Headlines at a lower level will be translated into a sectioning
+structure.  At a higher level, they will be translated into
+blocks.
+
+If an headline with a \"BEAMER_env\" property set to \"frame\" is
+found within a tree, its level locally overrides this number.
+
+This variable has no effect on headlines with the \"BEAMER_env\"
+property set to either \"ignoreheading\", \"appendix\", or
+\"note\", which will respectively, be invisible, become an
+appendix or a note.
+
+This integer is relative to the minimal level of an headline
+within the parse tree, defined as 1."
+  :group 'org-export-e-beamer
+  :type 'integer)
+
+(defcustom org-e-beamer-frame-default-options ""
+  "Default options string to use for frames.
+For example, it could be set to \"allowframebreaks\"."
+  :group 'org-export-e-beamer
+  :type '(string :tag "[options]"))
+
+(defcustom org-e-beamer-column-view-format
+  "%45ITEM %10BEAMER_env(Env) %10BEAMER_act(Act) %4BEAMER_col(Col) %8BEAMER_opt(Opt)"
+  "Column view format that should be used to fill the template."
+  :group 'org-export-e-beamer
+  :type '(choice
+	  (const  :tag "Do not insert Beamer column view format" nil)
+	  (string :tag "Beamer column view format")))
+
+(defcustom org-e-beamer-theme "default"
+  "Default theme used in Beamer presentations."
+  :group 'org-export-e-beamer
+  :type '(choice
+	  (const :tag "Do not insert a Beamer theme" nil)
+	  (string :tag "Beamer theme")))
+
+(defcustom org-e-beamer-environments-extra nil
+  "Environments triggered by tags in Beamer export.
+Each entry has 4 elements:
+
+name    Name of the environment
+key     Selection key for `org-e-beamer-select-environment'
+open    The opening template for the environment, with the following escapes
+        %a   the action/overlay specification
+        %A   the default action/overlay specification
+        %o   the options argument of the template
+        %h   the headline text
+        %H   if there is headline text, that text in {} braces
+        %U   if there is headline text, that text in [] brackets
+close   The closing string of the environment."
+  :group 'org-export-e-beamer
+  :type '(repeat
+	  (list
+	   (string :tag "Environment")
+	   (string :tag "Selection key")
+	   (string :tag "Begin")
+	   (string :tag "End"))))
+
+(defcustom org-e-beamer-outline-frame-title "Outline"
+  "Default title of a frame containing an outline."
+  :group 'org-export-e-beamer
+  :type '(string :tag "Outline frame title"))
+
+(defcustom org-e-beamer-outline-frame-options ""
+  "Outline frame options appended after \\begin{frame}.
+You might want to put e.g. \"allowframebreaks=0.9\" here."
+  :group 'org-export-e-beamer
+  :type '(string :tag "Outline frame options"))
+
+
+
+;;; Internal Variables
+
+(defconst org-e-beamer-column-widths
+  "0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0.0 :ETC"
+"The column widths that should be installed as allowed property values.")
+
+(defconst org-e-beamer-environments-special
+  '(("appendix"       "x")
+    ("column"         "c")
+    ("frame"          "f")
+    ("ignoreheading"  "i")
+    ("note"           "n")
+    ("noteNH"         "N"))
+  "Alist of environments treated in a special way by the back-end.
+Keys are environment names, as strings, values are bindings used
+in `org-e-beamer-select-environment'.  Environments listed here,
+along with their binding, are hard coded and cannot be modified
+through `org-e-beamer-environments-extra' variable.")
+
+(defconst org-e-beamer-environments-default
+  '(("block"          "b" "\\begin{block}%a{%h}"          "\\end{block}")
+    ("alertblock"     "a" "\\begin{alertblock}%a{%h}"     "\\end{alertblock}")
+    ("verse"          "v" "\\begin{verse}%a %% %h"        "\\end{verse}")
+    ("quotation"      "q" "\\begin{quotation}%a %% %h"    "\\end{quotation}")
+    ("quote"          "Q" "\\begin{quote}%a %% %h"        "\\end{quote}")
+    ("structureenv"   "s" "\\begin{structureenv}%a %% %h" "\\end{structureenv}")
+    ("theorem"        "t" "\\begin{theorem}%a%U"          "\\end{theorem}")
+    ("definition"     "d" "\\begin{definition}%a%U"       "\\end{definition}")
+    ("example"        "e" "\\begin{example}%a%U"          "\\end{example}")
+    ("exampleblock"   "E" "\\begin{exampleblock}%a{%h}"   "\\end{exampleblock}")
+    ("proof"          "p" "\\begin{proof}%a%U"            "\\end{proof}")
+    ("beamercolorbox" "o" "\\begin{beamercolorbox}%o{%h}" "\\end{beamercolorbox}"))
+  "Environments triggered by properties in Beamer export.
+These are the defaults - for user definitions, see
+`org-e-beamer-environments-extra'.")
+
+(defconst org-e-beamer-verbatim-elements
+  '(code example-block fixed-width inline-src-block src-block verbatim)
+  "List of element or object types producing verbatim text.
+This is used internally to determine when a frame should have the
+\"fragile\" option.")
+
+
+
+;;; Internal functions
+
+(defun org-e-beamer--normalize-argument (argument type)
+  "Return ARGUMENT string with proper boundaries.
+
+TYPE is a symbol among the following:
+`action'    Return ARGUMENT within angular brackets.
+`defaction' Return ARGUMENT within both square and angular brackets.
+`option'    Return ARGUMENT within square brackets."
+  (if (not (string-match "\\S-" argument)) ""
+    (case type
+      (action (if (string-match "\\`<.*>\\'" argument) argument
+		(format "<%s>" argument)))
+      (defaction (cond
+		  ((string-match "\\`\\[<.*>\\]\\'" argument) argument)
+		  ((string-match "\\`<.*>\\'" argument)
+		   (format "[%s]" argument))
+		  ((string-match "\\`\\[\\(.*\\)\\]\\'" argument)
+		   (format "[<%s>]" (match-string 1 argument)))
+		  (t (format "[<%s>]" argument))))
+      (option (if (string-match "\\`\\[.*\\]\\'" argument) argument
+		(format "[%s]" argument)))
+      (otherwise argument))))
+
+(defun org-e-beamer--element-has-overlay-p (element)
+  "Non-nil when ELEMENT has an overlay specified.
+An element has an overlay specification when it starts with an
+`e-beamer' export-snippet whose value is between angular
+brackets.  Return overlay specification, as a string, or nil."
+  (let ((first-object (car (org-element-contents element))))
+    (when (eq (org-element-type first-object) 'export-snippet)
+      (let ((value (org-element-property :value first-object)))
+	(and (string-match "\\`<.*>\\'" value) value)))))
+
+
+
+;;; Define Back-End
+
+(org-export-define-derived-backend e-beamer e-latex
+  :export-block "BEAMER"
+  :options-alist
+  ((:beamer-theme "BEAMER_THEME" nil org-e-beamer-theme)
+   (:beamer-color-theme "BEAMER_COLOR_THEME" nil nil t)
+   (:beamer-font-theme "BEAMER_FONT_THEME" nil nil t)
+   (:beamer-inner-theme "BEAMER_INNER_THEME" nil nil t)
+   (:beamer-outer-theme "BEAMER_OUTER_THEME" nil nil t)
+   (:headline-levels nil "H" org-e-beamer-frame-level))
+  :translate-alist ((bold . org-e-beamer-bold)
+		    (export-block . org-e-beamer-export-block)
+		    (export-snippet . org-e-beamer-export-snippet)
+		    (headline . org-e-beamer-headline)
+		    (item . org-e-beamer-item)
+		    (keyword . org-e-beamer-keyword)
+		    (link . org-e-beamer-link)
+		    (plain-list . org-e-beamer-plain-list)
+		    (radio-target . org-e-beamer-radio-target)
+		    (target . org-e-beamer-target)
+		    (template . org-e-beamer-template)))
+
+
+
+;;; Transcode Functions
+
+;;;; Bold
+
+(defun org-e-beamer-bold (bold contents info)
+  "Transcode BLOCK object into Beamer code.
+CONTENTS is the text being bold.  INFO is a plist used as
+a communication channel."
+  (format "\\alert%s{%s}"
+	  (or (org-e-beamer--element-has-overlay-p bold) "")
+	  contents))
+
+
+;;;; Export Block
+
+(defun org-e-beamer-export-block (export-block contents info)
+  "Transcode an EXPORT-BLOCK element into Beamer code.
+CONTENTS is nil.  INFO is a plist used as a communication
+channel."
+  (when (member (org-element-property :type export-block) '("BEAMER" "LATEX"))
+    (org-remove-indentation (org-element-property :value export-block))))
+
+
+;;;; Export Snippet
+
+(defun org-e-beamer-export-snippet (export-snippet contents info)
+  "Transcode an EXPORT-SNIPPET object into Beamer code.
+CONTENTS is nil.  INFO is a plist used as a communication
+channel."
+  (let ((backend (org-export-snippet-backend export-snippet))
+	(value (org-element-property :value export-snippet)))
+    ;; Only "e-latex" and "e-beamer" snippets are retained.
+    (cond ((eq backend 'e-latex) value)
+	  ;; Ignore "e-beamer" snippets specifying overlays.
+	  ((and (eq backend 'e-beamer)
+		(or (org-export-get-previous-element export-snippet info)
+		    (not (string-match "\\`<.*>\\'" value))))
+	   value))))
+
+
+;;;; Headline
+;;
+;; The main function to translate an headline is
+;; `org-e-beamer-headline'.
+;;
+;; Depending on the level at which an headline is considered as
+;; a frame (given by `org-e-beamer--frame-level'), the headline is
+;; either a section (`org-e-beamer--format-section'), a frame
+;; (`org-e-beamer--format-frame') or a block
+;; (`org-e-beamer--format-block').
+;;
+;; `org-e-beamer-headline' also takes care of special environments
+;; like "ignoreheading", "note", "noteNH" and "appendix".
+
+(defun org-e-beamer--frame-level (headline info)
+  "Return frame level in subtree containing HEADLINE.
+INFO is a plist used as a communication channel."
+  (or
+   ;; 1. Look for "frame" environment in parents, starting from the
+   ;;    farthest.
+   (catch 'exit
+     (mapc (lambda (parent)
+	     (when (equal (org-element-property :beamer-env parent) "frame")
+	       (throw 'exit (org-export-get-relative-level parent info))))
+	   (reverse (org-export-get-genealogy headline)))
+     nil)
+   ;; 2. Look for "frame" environment in HEADLINE.
+   (and (equal (org-element-property :beamer-env headline) "frame")
+	(org-export-get-relative-level headline info))
+   ;; 3. Look for "frame" environment in sub-tree.
+   (org-element-map
+    headline 'headline
+    (lambda (hl)
+      (when (equal (org-element-property :beamer-env hl) "frame")
+	(org-export-get-relative-level hl info)))
+    info 'first-match)
+   ;; 4. No "frame" environment in tree: use default value.
+   (plist-get info :headline-levels)))
+
+(defun org-e-beamer--format-section (headline contents info)
+  "Format HEADLINE as a sectioning part.
+CONTENTS holds the contents of the headline.  INFO is a plist
+used as a communication channel."
+  ;; Use `e-latex' back-end output, inserting overlay specifications
+  ;; if possible.
+  (let ((latex-headline
+	 (funcall (cdr (assq 'headline org-e-latex-translate-alist))
+		  headline contents info))
+	(mode-specs (org-element-property :beamer-act headline)))
+    (if (and mode-specs
+	     (string-match "\\`\\\\\\(.*?\\)\\(?:\\*\\|\\[.*\\]\\)?{"
+			   latex-headline))
+	(replace-match (concat (match-string 1 latex-headline)
+			       (format "<%s>" mode-specs))
+		       nil nil latex-headline 1)
+      latex-headline)))
+
+(defun org-e-beamer--format-frame (headline contents info)
+  "Format HEADLINE as a frame.
+CONTENTS holds the contents of the headline.  INFO is a plist
+used as a communication channel."
+  (let ((fragilep
+	 ;; FRAGILEP is non-nil when HEADLINE contains an element
+	 ;; among `org-e-beamer-verbatim-elements'.
+	 (org-element-map headline org-e-beamer-verbatim-elements 'identity
+			  info 'first-match)))
+    (concat "\\begin{frame}"
+	    ;; Overlay specification, if any. If is surrounded by square
+	    ;; brackets, consider it as a default specification.
+	    (let ((action (org-element-property :beamer-act headline)))
+	      (cond
+	       ((not action) "")
+	       ((string-match "\\`\\[.*\\]\\'" action )
+		(org-e-beamer--normalize-argument action 'defaction))
+	       (t (org-e-beamer--normalize-argument action 'action))))
+	    ;; Options, if any.
+	    (let ((options
+		   ;; Collect options from default value and headline's
+		   ;; properties.  Also add a label for links.
+		   (append
+		    (org-split-string org-e-beamer-frame-default-options
+				      ",")
+		    (let ((opt (org-element-property :beamer-opt headline)))
+		      (and opt (org-split-string
+				;; Remove square brackets if user
+				;; provided them.
+				(and (string-match "^\\[?\\(.*\\)\\]?$" opt)
+				     (match-string 1 opt))
+				",")))
+		    (list
+		     (format "label=sec-%s"
+			     (mapconcat
+			      'number-to-string
+			      (org-export-get-headline-number headline info)
+			      "-"))))))
+	      ;; Change options list into a string.
+	      (org-e-beamer--normalize-argument
+	       (mapconcat
+		'identity
+		(if (or (not fragilep) (member "fragile" options)) options
+		  (cons "fragile" options))
+		",")
+	       'option))
+	    ;; Title.
+	    (format "{%s}"
+		    (org-export-data (org-element-property :title headline)
+				     info))
+	    "\n"
+	    ;; The following workaround is required in fragile frames
+	    ;; as Beamer will append "\par" to the beginning of the
+	    ;; contents.  So we need to make sure the command is
+	    ;; separated from the contents by at least one space.  If
+	    ;; it isn't, it will create "\parfirst-word" command and
+	    ;; remove the first word from the contents in the PDF
+	    ;; output.
+	    (if (not fragilep) contents
+	      (replace-regexp-in-string "\\`\n*" "\\& " contents))
+	    "\\end{frame}")))
+
+(defun org-e-beamer--format-block (headline contents info)
+  "Format HEADLINE as a block.
+CONTENTS holds the contents of the headline.  INFO is a plist
+used as a communication channel."
+  (let* ((column-width (org-element-property :beamer-col headline))
+	 ;; Environment defaults to "block" if none is specified and
+	 ;; there is no column specification.  If there is a column
+	 ;; specified but still no explicit environment, ENVIRONMENT
+	 ;; is nil.
+	 (environment (let ((env (org-element-property :beamer-env headline)))
+			(cond
+			 ;; "block" is the fallback environment.
+			 ((and (not env) (not column-width)) "block")
+			 ;; "column" only.
+			 ((not env) nil)
+			 ;; Use specified environment.
+			 (t (downcase env)))))
+	 (env-format (when environment
+		       (assoc environment
+			      (append org-e-beamer-environments-special
+				      org-e-beamer-environments-extra
+				      org-e-beamer-environments-default))))
+	 (title (org-export-data (org-element-property :title headline) info))
+	 ;; Start a columns environment when there is no previous
+	 ;; headline or the previous headline do not have
+	 ;; a BEAMER_column property.
+	 (start-columns-p
+	  (and column-width
+	       (or (org-export-first-sibling-p headline info)
+		   (not (org-element-property
+			 :beamer-col
+			 (org-export-get-previous-element headline info))))))
+	 ;; Ends a columns environment when there is no next headline
+	 ;; or the next headline do not have a BEAMER_column property.
+	 (end-columns-p
+	  (and column-width
+	       (or (org-export-last-sibling-p headline info)
+		   (not (org-element-property
+			 :beamer-col
+			 (org-export-get-next-element headline info)))))))
+    (concat
+     (when start-columns-p "\\begin{columns}\n")
+     (when column-width
+       (format "\\begin{column}%s{%s}\n"
+	       ;; One can specify placement for column only when
+	       ;; HEADLINE stands for a column on its own.
+	       (if (not environment) ""
+		 (let ((options (org-element-property :beamer-opt headline)))
+		   (if (not options) ""
+		     (org-e-beamer--normalize-argument options 'option))))
+	       (format "%s\\textwidth" column-width)))
+     ;; Block's opening string.
+     (when env-format
+       (concat
+	(org-fill-template
+	 (nth 2 env-format)
+	 (nconc
+	  ;; If BEAMER_act property has its value enclosed in square
+	  ;; brackets, it is a default overlay specification and
+	  ;; overlay specification is empty.  Otherwise, it is an
+	  ;; overlay specification and the default one is nil.
+	  (let ((action (org-element-property :beamer-act headline)))
+	    (cond
+	     ((not action) (list (cons "a" "") (cons "A" "")))
+	     ((string-match "\\`\\[.*\\]\\'" action)
+	      (list
+	       (cons "A"
+		     (org-e-beamer--normalize-argument action 'defaction))
+	       (cons "a" "")))
+	     (t
+	      (list
+	       (cons "a"
+		     (org-e-beamer--normalize-argument action 'action))
+	       (cons "A" "")))))
+	  (list (cons "o"
+		      (let ((options
+			     (org-element-property :beamer-opt headline)))
+			(if (not options) ""
+			  (org-e-beamer--normalize-argument options 'option))))
+		(cons "h" title)
+		(cons "H" (if (equal title "") "" (format "{%s}" title)))
+		(cons "U" (if (equal title "") "" (format "[%s]" title))))))
+	"\n"))
+     contents
+     ;; Block's closing string.
+     (when environment (concat (nth 3 env-format) "\n"))
+     (when column-width "\\end{column}\n")
+     (when end-columns-p "\\end{columns}"))))
+
+(defun org-e-beamer-headline (headline contents info)
+  "Transcode HEADLINE element into Beamer code.
+CONTENTS is the contents of the headline.  INFO is a plist used
+as a communication channel."
+  (unless (org-element-property :footnote-section-p headline)
+    (let ((level (org-export-get-relative-level headline info))
+	  (frame-level (org-e-beamer--frame-level headline info))
+	  (environment (let ((env (org-element-property :beamer-env headline)))
+			 (if (stringp env) (downcase env) "block"))))
+      (cond
+       ;; Creation of an appendix is requested.
+       ((equal environment "appendix")
+	(concat "\\appendix"
+		(org-element-property :beamer-act headline)
+		"\n"
+		(make-string (org-element-property :pre-blank headline) ?\n)
+		contents))
+       ((equal environment "ignoreheading")
+	(concat (make-string (org-element-property :pre-blank headline) ?\n)
+		contents))
+       ;; HEADLINE is a note.
+       ((member environment '("note" "noteNH"))
+	(format "\\note{%s}"
+		(concat (and (equal environment "note")
+			     (concat
+			      (org-export-data
+			       (org-element-property :title headline) info)
+			      "\n"))
+			(org-trim contents))))
+       ;; HEADLINE is a frame.
+       ((or (equal environment "frame") (= level frame-level))
+	(org-e-beamer--format-frame headline contents info))
+       ;; Regular section, extracted from `org-e-latex-classes'.
+       ((< level frame-level)
+	(org-e-beamer--format-section headline contents info))
+       ;; Otherwise, HEADLINE is a block.
+       (t (org-e-beamer--format-block headline contents info))))))
+
+
+;;;; Item
+
+(defun org-e-beamer-item (item contents info)
+  "Transcode an ITEM element into Beamer code.
+CONTENTS holds the contents of the item.  INFO is a plist holding
+contextual information."
+  (let ((action (let ((first-element (car (org-element-contents item))))
+		  (and (eq (org-element-type first-element) 'paragraph)
+		       (org-e-beamer--element-has-overlay-p first-element))))
+	(output (funcall (cdr (assq 'item org-e-latex-translate-alist))
+			 item contents info)))
+    (if (not action) output
+      ;; If the item starts with a paragraph and that paragraph starts
+      ;; with an export snippet specifying an overlay, insert it after
+      ;; \item command.
+      (replace-regexp-in-string "\\\\item" (concat "\\\\item" action) output))))
+
+
+;;;; Keyword
+
+(defun org-e-beamer-keyword (keyword contents info)
+  "Transcode a KEYWORD element into Beamer code.
+CONTENTS is nil.  INFO is a plist used as a communication
+channel."
+  (let ((key (org-element-property :key keyword))
+	(value (org-element-property :value keyword)))
+    ;; Handle specifically BEAMER and TOC (headlines only) keywords.
+    ;; Otherwise, fallback to `e-latex' back-end.
+    (cond
+     ((equal key "BEAMER") value)
+     ((and (equal key "TOC") (string-match "\\<headlines\\>" value))
+      (let ((depth (or (and (string-match "[0-9]+" value)
+			    (string-to-number (match-string 0 value)))
+		       (plist-get info :with-toc)))
+	    (options (and (string-match "\\[.*?\\]" value)
+			  (match-string 0 value))))
+	(concat
+	 "\\begin{frame}"
+	 (when (wholenump depth) (format "\\setcounter{tocdepth}{%s}\n" depth))
+	 "\\tableofcontents" options "\n"
+	 "\\end{frame}")))
+     (t (funcall (cdr (assq 'keyword org-e-latex-translate-alist))
+		 keyword contents info)))))
+
+
+;;;; Link
+
+(defun org-e-beamer-link (link contents info)
+  "Transcode a LINK object into Beamer code.
+CONTENTS is the description part of the link.  INFO is a plist
+used as a communication channel."
+  (let ((type (org-element-property :type link))
+	(path (org-element-property :path link)))
+    ;; Use \hyperlink command for all internal links.
+    (cond
+     ((equal type "radio")
+      (let ((destination (org-export-resolve-radio-link link info)))
+	(when destination
+	  (format "\\hyperlink%s{%s}{%s}"
+		  (or (org-e-beamer--element-has-overlay-p link) "")
+		  (org-export-solidify-link-text path)
+		  (org-export-data (org-element-contents destination) info)))))
+     ((and (member type '("custom-id" "fuzzy" "id"))
+	   (let ((destination (if (string= type "fuzzy")
+				  (org-export-resolve-fuzzy-link link info)
+				(org-export-resolve-id-link link info))))
+	     (case (org-element-type destination)
+	       (headline
+		(let ((label
+		       (format "sec-%s"
+			       (mapconcat
+				'number-to-string
+				(org-export-get-headline-number
+				 destination info)
+				"-"))))
+		  (if (and (plist-get info :section-numbers) (not contents))
+		      (format "\\ref{%s}" label)
+		    (format "\\hyperlink%s{%s}{%s}"
+			    (or (org-e-beamer--element-has-overlay-p link) "")
+			    label
+			    contents))))
+	       (target
+		(let ((path (org-export-solidify-link-text path)))
+		  (if (not contents) (format "\\ref{%s}" path)
+		    (format "\\hyperlink%s{%s}{%s}"
+			    (or (org-e-beamer--element-has-overlay-p link) "")
+			    path
+			    contents))))))))
+     ;; Otherwise, use `e-latex' back-end.
+     (t (funcall (cdr (assq 'link org-e-latex-translate-alist))
+		 link contents info)))))
+
+
+;;;; Plain List
+;;
+;; Plain lists support `:overlay' (for any type), `:template' (for
+;; ordered lists only) and `:long-text' (for description lists only)
+;; attributes.
+
+(defun org-e-beamer-plain-list (plain-list contents info)
+  "Transcode a PLAIN-LIST element into Beamer code.
+CONTENTS is the contents of the list.  INFO is a plist holding
+contextual information."
+  (let* ((type (org-element-property :type plain-list))
+	 (attributes (org-export-read-attribute :attr_beamer plain-list))
+	 (latex-type (cond ((eq type 'ordered) "enumerate")
+			   ((eq type 'descriptive) "description")
+			   (t "itemize"))))
+    (org-e-latex--wrap-label
+     plain-list
+     (format "\\begin{%s}%s%s\n%s\\end{%s}"
+	     latex-type
+	     ;; Default overlay specification, if any.
+	     (let ((overlay (plist-get attributes :overlay)))
+	       (if (not overlay) ""
+		 (org-e-beamer--normalize-argument overlay 'defaction)))
+	     ;; Second optional argument depends on the list type.
+	     (case type
+	       (ordered
+		(let ((template (plist-get attributes :template)))
+		  (if (not template) ""
+		    (org-e-beamer--normalize-argument template 'option))))
+	       (descriptive
+		(let ((long-text (plist-get attributes :long-text)))
+		  (if (not long-text) ""
+		    (org-e-beamer--normalize-argument long-text 'option))))
+	       ;; There's no second argument for un-ordered lists.
+	       (otherwise ""))
+	     ;; Eventually insert contents and close environment.
+	     contents
+	     latex-type))))
+
+
+;;;; Radio Target
+
+(defun org-e-beamer-radio-target (radio-target text info)
+  "Transcode a RADIO-TARGET object into Beamer code.
+TEXT is the text of the target.  INFO is a plist holding
+contextual information."
+  (format "\\hypertarget%s{%s}{%s}"
+	  (or (org-e-beamer--element-has-overlay-p radio-target) "")
+	  (org-export-solidify-link-text
+	   (org-element-property :value radio-target))
+	  text))
+
+
+;;;; Target
+
+(defun org-e-beamer-target (target contents info)
+  "Transcode a TARGET object into Beamer code.
+CONTENTS is nil.  INFO is a plist holding contextual
+information."
+  (format "\\hypertarget{%s}{}"
+	  (org-export-solidify-link-text (org-element-property :value target))))
+
+
+;;;; Template
+;;
+;; Template used is similar to the one used in `e-latex' back-end,
+;; excepted for the table of contents and Beamer themes.
+
+(defun org-e-beamer-template (contents info)
+  "Return complete document string after Beamer conversion.
+CONTENTS is the transcoded contents string.  INFO is a plist
+holding export options."
+  (let ((title (org-export-data (plist-get info :title) info)))
+    (concat
+     ;; 1. Time-stamp.
+     (and (plist-get info :time-stamp-file)
+	  (format-time-string "%% Created %Y-%m-%d %a %H:%M\n"))
+     ;; 2. Document class and packages.
+     (let ((class (plist-get info :latex-class))
+	   (class-options (plist-get info :latex-class-options)))
+       (org-element-normalize-string
+	(let* ((header (nth 1 (assoc class org-e-latex-classes)))
+	       (document-class-string
+		(and (stringp header)
+		     (if class-options
+			 (replace-regexp-in-string
+			  "^[ \t]*\\\\documentclass\\(\\[.*?\\]\\)"
+			  class-options header t nil 1)
+		       header))))
+	  (when document-class-string
+	    (org-e-latex--guess-babel-language
+	     (org-e-latex--guess-inputenc
+	      (org-splice-latex-header
+	       document-class-string
+	       org-export-latex-default-packages-alist ; defined in org.el
+	       org-export-latex-packages-alist nil ; defined in org.el
+	       (plist-get info :latex-header-extra)))
+	     info)))))
+     ;; 3. Insert themes.
+     (let ((format-theme
+	    (function
+	     (lambda (prop command)
+	       (let ((theme (plist-get info prop)))
+		 (when theme
+		   (concat command
+			   (if (not (string-match "\\[.*\\]" theme))
+			       (format "{%s}\n" theme)
+			     (format "%s{%s}\n"
+				     (match-string 0 theme)
+				     (org-trim
+				      (replace-match "" nil nil theme)))))))))))
+       (mapconcat (lambda (args) (apply format-theme args))
+		  '((:beamer-theme "\\usetheme")
+		    (:beamer-color-theme "\\usecolortheme")
+		    (:beamer-font-theme "\\usefonttheme")
+		    (:beamer-inner-theme "\\useinnertheme")
+		    (:beamer-outer-theme "\\useoutertheme"))
+		  ""))
+     ;; 4. Possibly limit depth for headline numbering.
+     (let ((sec-num (plist-get info :section-numbers)))
+       (when (integerp sec-num)
+	 (format "\\setcounter{secnumdepth}{%d}\n" sec-num)))
+     ;; 5. Author.
+     (let ((author (and (plist-get info :with-author)
+			(let ((auth (plist-get info :author)))
+			  (and auth (org-export-data auth info)))))
+	   (email (and (plist-get info :with-email)
+		       (org-export-data (plist-get info :email) info))))
+       (cond ((and author email (not (string= "" email)))
+	      (format "\\author{%s\\thanks{%s}}\n" author email))
+	     (author (format "\\author{%s}\n" author))
+	     (t "\\author{}\n")))
+     ;; 6. Date.
+     (format "\\date{%s}\n" (org-export-data (plist-get info :date) info))
+     ;; 7. Title
+     (format "\\title{%s}\n" title)
+     ;; 8. Hyperref options.
+     (format "\\hypersetup{\n  pdfkeywords={%s},\n  pdfsubject={%s},\n  pdfcreator={%s}}\n"
+	     (or (plist-get info :keywords) "")
+	     (or (plist-get info :description) "")
+	     (if (not (plist-get info :with-creator)) ""
+	       (plist-get info :creator)))
+     ;; 9. Document start.
+     "\\begin{document}\n\n"
+     ;; 10. Title command.
+     (org-element-normalize-string
+      (cond ((string= "" title) nil)
+	    ((not (stringp org-e-latex-title-command)) nil)
+	    ((string-match "\\(?:[^%]\\|^\\)%s"
+			   org-e-latex-title-command)
+	     (format org-e-latex-title-command title))
+	    (t org-e-latex-title-command)))
+     ;; 11. Table of contents.
+     (let ((depth (plist-get info :with-toc)))
+       (when depth
+	 (concat
+	  (format "\\begin{frame}%s{%s}\n"
+		  (org-e-beamer--normalize-argument
+		   org-e-beamer-outline-frame-options 'option)
+		  org-e-beamer-outline-frame-title)
+	  (when (wholenump depth)
+	    (format "\\setcounter{tocdepth}{%d}\n" depth))
+	  "\\tableofcontents\n"
+	  "\\end{frame}\n\n")))
+     ;; 12. Document's body.
+     contents
+     ;; 13. Creator.
+     (let ((creator-info (plist-get info :with-creator)))
+       (cond
+	((not creator-info) "")
+	((eq creator-info 'comment)
+	 (format "%% %s\n" (plist-get info :creator)))
+	(t (concat (plist-get info :creator) "\n"))))
+     ;; 14. Document end.
+     "\\end{document}")))
+
+
+
+;;; Minor Mode
+
+
+(defvar org-e-beamer-mode-map (make-sparse-keymap)
+  "The keymap for `org-e-beamer-mode'.")
+(define-key org-e-beamer-mode-map "\C-c\C-b" 'org-e-beamer-select-environment)
+
+;;;###autoload
+(define-minor-mode org-e-beamer-mode
+  "Support for editing Beamer oriented Org mode files."
+  nil " Bm" 'org-e-beamer-mode-map)
+
+(when (fboundp 'font-lock-add-keywords)
+  (font-lock-add-keywords
+   'org-mode
+   '((":\\(B_[a-z]+\\|BMCOL\\):" 1 'org-e-beamer-tag prepend))
+   'prepend))
+
+(defface org-e-beamer-tag '((t (:box (:line-width 1 :color grey40))))
+  "The special face for beamer tags."
+  :group 'org-export-e-beamer)
+
+(defun org-e-beamer-property-changed (property value)
+  "Track the BEAMER_env property with tags.
+PROPERTY is the name of the modified property.  VALUE is its new
+value."
+  (cond
+   ((equal property "BEAMER_env")
+    (save-excursion
+      (org-back-to-heading t)
+      (let ((tags (org-get-tags)))
+	(setq tags (delq nil (mapcar (lambda (x)
+				       (if (string-match "^B_" x) nil x))
+				     tags)))
+	(org-set-tags-to tags))
+      (when (org-string-nw-p value) (org-toggle-tag (concat "B_" value) 'on))))
+   ((equal property "BEAMER_col")
+    (org-toggle-tag "BMCOL" (if (org-string-nw-p value) 'on 'off)))))
+
+(add-hook 'org-property-changed-functions 'org-e-beamer-property-changed)
+
+(defun org-e-beamer-allowed-property-values (property)
+  "Supply allowed values for PROPERTY."
+  (cond
+   ((and (equal property "BEAMER_env")
+	 (not (org-entry-get nil (concat property "_ALL") 'inherit)))
+    ;; If no allowed values for BEAMER_env have been defined,
+    ;; supply all defined environments
+    (mapcar 'car (append org-e-beamer-environments-special
+			 org-e-beamer-environments-extra
+			 org-e-beamer-environments-default)))
+   ((and (equal property "BEAMER_col")
+	 (not (org-entry-get nil (concat property "_ALL") 'inherit)))
+    ;; If no allowed values for BEAMER_col have been defined,
+    ;; supply some
+    (org-split-string org-e-beamer-column-widths " "))))
+
+(add-hook 'org-property-allowed-value-functions
+	  'org-e-beamer-allowed-property-values)
+
+
+
+;;; Commands
+
+;;;###autoload
+(defun org-e-beamer-export-as-latex
+  (&optional subtreep visible-only body-only ext-plist)
+  "Export current buffer as a Beamer buffer.
+
+If narrowing is active in the current buffer, only export its
+narrowed part.
+
+If a region is active, export that region.
+
+When optional argument SUBTREEP is non-nil, export the sub-tree
+at point, extracting information from the headline properties
+first.
+
+When optional argument VISIBLE-ONLY is non-nil, don't export
+contents of hidden elements.
+
+When optional argument BODY-ONLY is non-nil, only write code
+between \"\\begin{document}\" and \"\\end{document}\".
+
+EXT-PLIST, when provided, is a property list with external
+parameters overriding Org default settings, but still inferior to
+file-local settings.
+
+Export is done in a buffer named \"*Org E-BEAMER Export*\", which
+will be displayed when `org-export-show-temporary-export-buffer'
+is non-nil."
+  (interactive)
+  (let ((outbuf (org-export-to-buffer
+		 'e-beamer "*Org E-BEAMER Export*"
+		 subtreep visible-only body-only ext-plist)))
+    (with-current-buffer outbuf (LaTeX-mode))
+    (when org-export-show-temporary-export-buffer
+      (switch-to-buffer-other-window outbuf))))
+
+;;;###autoload
+(defun org-e-beamer-export-to-latex
+  (&optional subtreep visible-only body-only ext-plist pub-dir)
+  "Export current buffer as a Beamer presentation (tex).
+
+If narrowing is active in the current buffer, only export its
+narrowed part.
+
+If a region is active, export that region.
+
+When optional argument SUBTREEP is non-nil, export the sub-tree
+at point, extracting information from the headline properties
+first.
+
+When optional argument VISIBLE-ONLY is non-nil, don't export
+contents of hidden elements.
+
+When optional argument BODY-ONLY is non-nil, only write code
+between \"\\begin{document}\" and \"\\end{document}\".
+
+EXT-PLIST, when provided, is a property list with external
+parameters overriding Org default settings, but still inferior to
+file-local settings.
+
+When optional argument PUB-DIR is set, use it as the publishing
+directory.
+
+Return output file's name."
+  (interactive)
+  (let ((outfile (org-export-output-file-name ".tex" subtreep pub-dir)))
+    (org-export-to-file
+     'e-beamer outfile subtreep visible-only body-only ext-plist)))
+
+;;;###autoload
+(defun org-e-beamer-export-to-pdf
+  (&optional subtreep visible-only body-only ext-plist pub-dir)
+  "Export current buffer as a Beamer presentation (PDF).
+
+If narrowing is active in the current buffer, only export its
+narrowed part.
+
+If a region is active, export that region.
+
+When optional argument SUBTREEP is non-nil, export the sub-tree
+at point, extracting information from the headline properties
+first.
+
+When optional argument VISIBLE-ONLY is non-nil, don't export
+contents of hidden elements.
+
+When optional argument BODY-ONLY is non-nil, only write code
+between \"\\begin{document}\" and \"\\end{document}\".
+
+EXT-PLIST, when provided, is a property list with external
+parameters overriding Org default settings, but still inferior to
+file-local settings.
+
+When optional argument PUB-DIR is set, use it as the publishing
+directory.
+
+Return PDF file's name."
+  (interactive)
+  (org-e-latex-compile
+   (org-e-beamer-export-to-latex
+    subtreep visible-only body-only ext-plist pub-dir)))
+
+;;;###autoload
+(defun org-e-beamer-select-environment ()
+  "Select the environment to be used by beamer for this entry.
+While this uses (for convenience) a tag selection interface, the
+result of this command will be that the BEAMER_env *property* of
+the entry is set.
+
+In addition to this, the command will also set a tag as a visual
+aid, but the tag does not have any semantic meaning."
+  (interactive)
+  ;; Make sure `org-e-beamer-environments-special' has a higher
+  ;; priority than `org-e-beamer-environments-extra'.
+  (let* ((envs (append org-e-beamer-environments-special
+		       org-e-beamer-environments-extra
+		       org-e-beamer-environments-default))
+	 (org-tag-alist
+	  (append '((:startgroup))
+		  (mapcar (lambda (e) (cons (concat "B_" (car e))
+				       (string-to-char (nth 1 e))))
+			  envs)
+		  '((:endgroup))
+		  '(("BMCOL" . ?|))))
+	 (org-fast-tag-selection-single-key t))
+    (org-set-tags)
+    (let ((tags (or (ignore-errors (org-get-tags-string)) "")))
+      (cond
+       ((eq org-last-tag-selection-key ?|)
+	(if (string-match ":BMCOL:" tags)
+	    (org-set-property "BEAMER_col" (read-string "Column width: "))
+	  (org-delete-property "BEAMER_col")))
+       ((string-match (concat ":B_\\("
+			      (mapconcat 'car envs "\\|")
+			      "\\):")
+		      tags)
+	(org-entry-put nil "BEAMER_env" (match-string 1 tags)))
+       (t (org-entry-delete nil "BEAMER_env"))))))
+
+;;;###autoload
+(defun org-e-beamer-insert-options-template (&optional kind)
+  "Insert a settings template, to make sure users do this right."
+  (interactive (progn
+		 (message "Current [s]ubtree or [g]lobal?")
+		 (if (eq (read-char-exclusive) ?g) (list 'global)
+		   (list 'subtree))))
+  (if (eq kind 'subtree)
+      (progn
+	(org-back-to-heading t)
+	(org-reveal)
+	(org-entry-put nil "EXPORT_LaTeX_CLASS" "beamer")
+	(org-entry-put nil "EXPORT_LaTeX_CLASS_OPTIONS" "[presentation]")
+	(org-entry-put nil "EXPORT_FILE_NAME" "presentation.pdf")
+	(when org-e-beamer-column-view-format
+	  (org-entry-put nil "COLUMNS" org-e-beamer-column-view-format))
+	(org-entry-put nil "BEAMER_col_ALL" org-e-beamer-column-widths))
+    (insert "#+LaTeX_CLASS: beamer\n")
+    (insert "#+LaTeX_CLASS_OPTIONS: [presentation]\n")
+    (when org-e-beamer-theme
+      (insert "#+BEAMER_THEME: " org-e-beamer-theme "\n"))
+    (when org-e-beamer-column-view-format
+      (insert "#+COLUMNS: " org-e-beamer-column-view-format "\n"))
+    (insert "#+PROPERTY: BEAMER_col_ALL " org-e-beamer-column-widths "\n")))
+
+
+(provide 'org-e-beamer)
+;;; org-e-beamer.el ends here