3. Labels and References

LaTeX provides a powerful mechanism to deal with cross--references in a document. When writing a document, any part of it can be marked with a label, like `\label{mark}'. LaTeX records the current value of a certain counter when a label is defined. Later references to this label (like `\ref{mark}') will produce the recorded value of the counter.

Labels can be used to mark sections, figures, tables, equations, footnotes, items in enumerate lists etc. LaTeX is context sensitive in doing this: A label defined in a figure environment automatically records the figure counter, not the section counter.

Several different environments can share a common counter and therefore a common label category. E.g. labels in both equation and eqnarray environments record the value of the same counter - the equation counter.

3.1 Creating Labels

In order to create a label in a LaTeX document, press C-c ( (reftex-label). Just like LaTeX, RefTeX is context sensitive and will figure out the environment it currently is in and adapt the label to that environment. A label usually consists of a short prefix indicating the type of the label and a unique mark. RefTeX has 3 different modes to create this mark.

1. A label can be derived from context. This means, RefTeX takes the context of the label definition and constructs a label from that(1). This works best for section labels, where the section heading is used to construct a label. In fact, RefTeX's default settings use this method only for section labels. You will be asked to confirm the derived label, or edit it.

2. We may also use a simple unique number to identify a label. This is mostly useful for labels where it is difficult to come up with a very good descriptive name. RefTeX's default settings use this method for equations, enumerate items and footnotes. The author of RefTeX tends to write documents with many equations and finds it impossible to come up with good names for each of them. These simple labels are inserted without query, and are therefore very fast. Good descriptive names are not really necessary as RefTeX will provide context to reference a label (see section 3.2 Referencing Labels).

3. The third method is to ask the user for a label. This is most useful for things which are easy to describe briefly and do not turn up too frequently in a document. RefTeX uses this for figures and tables. Of course, one can enter the label directly by typing the full `\label{mark}'. The advantage of using reftex-label anyway is that RefTeX will know that a new label has been defined. It will then not be necessary to rescan the document in order to access this label later.

If you want to change the way certain labels are created, check out the variable reftex-insert-label-flags (see section 8.3 Creating Labels).

If you are using AUCTeX to write your LaTeX documents, you can set it up to delegate the creation of labels to RefTeX. See section 6.8 AUC TeX, for more information.

3.2 Referencing Labels

Referencing Labels is really at the heart of RefTeX. Press C-c ) in order to reference a label (reftex-reference). This will start a selection process and finally insert the complete `\ref{label}' into the buffer.

First, RefTeX will determine the label category which is required. Often that can be figured out from context. For example, if you write `As shown in eq.' and the press C-c ), RefTeX knows that an equation label is going to be referenced. If it cannot figure out what label category is needed, it will query for one.

You will then be presented with a label selection menu. This is a special buffer which contains an outline of the document along with all labels of the given label category. In addition, next to the label there will be one line of context of the label definition, which is some text in the buffer near the label definition. Usually this is sufficient to identify the label. If you are unsure about a certain label, pressing SPC will show the label definition point in another window.

In order to reference a label, move to cursor to the correct label and press RET. You can also reference several labels with a single call to reftex-reference by marking entries with the m key (see below).

Here is a list of special commands in the selection buffer. A summary of this information is always available from the selection process by pressing ?.

General

General

? Show a summary of available commands.

0-9,- Prefix argument.

Moving around

Moving around

n Go to next label.

p Go to previous label.

b Jump back to the position where you last left the selection buffer. Normally this should get you back to the last referenced label.

C-c C-n Goto next section heading.

C-c C-p Goto previous section heading.

N z Jump to section N, using the prefix arg. For example 3 z jumps to section 3.

Displaying Context

Displaying Context

SPC Show the surroundings of the definition of the current label in another window. See also the f key.

f Toggle follow mode. When follow mode is active, the other window will always display the full context of the current label. This is similar to pressing SPC after each cursor motion. Note that only context in files already visited is shown. RefTeX will not visit a file just for follow mode. See, however, the variable reftex-revisit-to-follow.

. Show insertion point in another window. This is the point from where you called reftex-reference.

Selecting a label and creating the reference

Selecting a label and creating the reference

RET Insert a reference to the label at point into the buffer from which the selection process was started. When entries have been marked, RET references all marked labels.

mouse-2 Clicking with mouse button 2 on a label will accept it like RET would. See also variable reftex-highlight-selection, 8.11 Miscellaneous.

m - + , Mark the current entry. When several entries have been marked, pressing RET will accept all of them and place them into several \ref macros. The special markers `,-+' also store a separator to be inserted before the corresponding reference. So marking six entries with the keys `m , , - , +' will give a reference list like this (see the variable reftex-multiref-punctuation)

In eqs. (1), (2), (3)--(4), (5) and (6)

u Unmark a marked entry.

a Accept the marked entries and put all labels as a comma-separated list into one single \ref macro. Some packages like `saferef.sty' support multiple references in this way.

l Use the last referenced label(s) again. This is equivalent to moving to that label and pressing RET.

TAB Enter a label with completion. This may also be a label which does not yet exist in the document.

v Toggle between \ref and \vref macro for references. The \vref macro is defined in the varioref LaTeX package. With this key you can force RefTeX to insert a \vref macro. The current state of this flag is displayed by the `S<>' indicator in the mode line of the selection buffer.

V Cycle between \ref, \fref and \Fref. The \fref and \Fref macros are defined in the fancyref LaTeX package. With this key you can force RefTeX to insert a \fref or \Fref macro. The current state of this flag is displayed by the `S<>' indicator in the mode line of the selection buffer.

Exiting

Exiting

q Exit the selection process without inserting any reference into the buffer.

Controlling what gets displayed

Controlling what gets displayed The defaults for the following flags can be configured with the variable reftex-label-menu-flags (see section 8.4 Referencing Labels).

c Toggle the display of the one-line label definition context in the selection buffer.

F Toggle the display of the file borders of a multifile document in the selection buffer.

t Toggle the display of the table of contents in the selection buffer. With prefix arg, change the maximum level of toc entries displayed to arg. Chapters are level 1, section are level 2.

# Toggle the display of a label counter in the selection buffer.

% Toggle the display of labels hidden in comments in the selection buffers. Sometimes, you may have commented out parts of your document. If these parts contain label definitions, RefTeX can still display and reference these labels.

Updating the buffer

Updating the buffer

g Update the menu. This will rebuilt the menu from the internal label list, but not reparse the document (see r).

r Reparse the document to update the information on all labels and rebuild the menu. If the variable reftex-enable-partial-scans is non-nil and your document is a multifile document, this will reparse only a part of the document (the file in which the label at point was defined).

C-u r Reparse the entire document.

s Switch the label category. After prompting for another label category, a menu for that category will be shown.

x Reference a label from an external document. With the LaTeX package xr it is possible to reference labels defined in another document. This key will switch to the label menu of an external document and let you select a label from there (see section xr).

In order to define additional commands for the selection process, the keymap reftex-select-label-map may be used.

3.3 Builtin Label Environments

RefTeX needs to be aware of the environments which can be referenced with a label (i.e. which carry their own counters). By default, RefTeX recognizes all labeled environments and macros discussed in The LaTeX Companion by Goossens, Mittelbach & Samarin, Addison-Wesley 1994.. These are:

• figure, figure*, table, table*, equation, eqnarray, enumerate, the \footnote macro (this is the LaTeX core stuff)
• align, gather, multline, flalign, alignat, xalignat, xxalignat, subequations (from AMS-LaTeX's `amsmath.sty' package)
• the \endnote macro (from `endnotes.sty')
• Beqnarray (`fancybox.sty')
• floatingfig (`floatfig.sty')
• longtable (`longtable.sty')
• figwindow, tabwindow (`picinpar.sty')
• SCfigure, SCtable (`sidecap.sty')
• sidewaysfigure, sidewaystable (`rotating.sty')
• subfigure, subfigure*, the \subfigure macro (`subfigure.sty')
• supertabular (`supertab.sty')
• wrapfigure (`wrapfig.sty')

If you want to use other labeled environments, defined with \newtheorem, RefTeX needs to be configured to recognize them (see section 3.4 Defining Label Environments).

3.4 Defining Label Environments

RefTeX can be configured to recognize additional labeled environments and macros. This is done with the variable reftex-label-alist (see section 8.2 Defining Label Environments). If you are not familiar with Lisp, you can use the custom library to configure this rather complex variable. To do this, use

M-x customize-variable RET reftex-label-alist RET

Here we will discuss a few examples, in order to make things clearer. It can also be instructive to look at the constant reftex-label-alist-builtin which contains the entries for all the builtin environments and macros (see section 3.3 Builtin Label Environments).

3.4.1 Theorem and Axiom Environments

Suppose you are using \newtheorem in LaTeX in order to define two new environments, theorem and axiom

\newtheorem{axiom}{Axiom}
\newtheorem{theorem}{Theorem}

to be used like this:

\begin{axiom}
\label{ax:first}
  ....
\end{axiom}

So we need to tell RefTeX that theorem and axiom are new labeled environments which define their own label categories. We can either use Lisp to do this (e.g. in `.emacs') or use the custom library. With Lisp it would look like this

(setq reftex-label-alist
   '(("axiom"   ?a "ax:"  "~\\ref{%s}" nil ("axiom"   "ax.") -2)
     ("theorem" ?h "thr:" "~\\ref{%s}" t   ("theorem" "th.") -3)))

The type indicator characters ?a and ?h are used for prompts when RefTeX queries for a label type. ?h was chosen for theorem since ?t is already taken by table. Note that also ?s, ?f, ?e, ?i, ?n are already used for standard environments.

The labels for Axioms and Theorems will have the prefixes `ax:' and `thr:', respectively. See section 6.8 AUC TeX, for information on how AUCTeX can use RefTeX to automatically create labels when a new environment is inserted into a buffer. Additionally, the following needs to be added to one's .emacs file before AUCTeX will automatically create labels for the new environments.

(add-hook 'LaTeX-mode-hook
   (lambda ()
     (LaTeX-add-environments
       '("axiom" LaTeX-env-label)
       '("theorem" LaTeX-env-label))))

The `~\ref{%s}' is a format string indicating how to insert references to these labels.

The next item indicates how to grab context of the label definition.

• t means to get it from a default location (from the beginning of a \macro or after the \begin statement). t is not a good choice for eqnarray and similar environments.
• nil means to use the text right after the label definition.
• For more complex ways of getting context, see the variable reftex-label-alist (8.2 Defining Label Environments).

The following list of strings is used to guess the correct label type from the word before point when creating a reference. E.g. if you write: `As we have shown in Theorem' and then press C-c ), RefTeX will know that you are looking for a theorem label and restrict the menu to only these labels without even asking.

The final item in each entry is the level at which the environment should produce entries in the table of context buffer. If the number is positive, the environment will produce numbered entries (like \section), if it is negative the entries will be unnumbered (like \section*). Use this only for environments which structure the document similar to sectioning commands. For everything else, omit the item.

To do the same configuration with customize, you need to click on the [INS] button twice to create two templates and fill them in like this:

Reftex Label Alist: [Hide]
[INS] [DEL] Package or Detailed   : [Value Menu] Detailed:
            Environment or \macro : [Value Menu] String: axiom
            Type specification    : [Value Menu] Char  : a
            Label prefix string   : [Value Menu] String: ax:
            Label reference format: [Value Menu] String: ~\ref{%s}
            Context method        : [Value Menu] After label
            Magic words:
              [INS] [DEL] String: axiom
              [INS] [DEL] String: ax.
              [INS]
            [X] Make TOC entry    : [Value Menu] Level: -2
[INS] [DEL] Package or Detailed   : [Value Menu] Detailed:
            Environment or \macro : [Value Menu] String: theorem
            Type specification    : [Value Menu] Char  : h
            Label prefix string   : [Value Menu] String: thr:
            Label reference format: [Value Menu] String: ~\ref{%s}
            Context method        : [Value Menu] Default position
            Magic words:
              [INS] [DEL] String: theorem
              [INS] [DEL] String: theor.
              [INS] [DEL] String: th.
              [INS]
            [X] Make TOC entry    : [Value Menu] Level: -3

Depending on how you would like the label insertion and selection for the new environments to work, you might want to add the letters `a' and `h' to some of the flags in the variables reftex-insert-label-flags (see section 8.3 Creating Labels) and reftex-label-menu-flags (see section 8.4 Referencing Labels).

3.4.2 Quick Equation Macro

Suppose you would like to have a macro for quick equations. It could be defined like this:

\newcommand{\quickeq}[1]{\begin{equation} #1 \end{equation}}

and used like this:

Einstein's equation is \quickeq{E=mc^2 \label{eq:einstein}}.

We need to tell RefTeX that any label defined in the argument of the \quickeq is an equation label. Here is how to do this with lisp:

(setq reftex-label-alist '(("\\quickeq{}" ?e nil nil 1 nil)))

The first element in this list is now the macro with empty braces as an image of the macro arguments. ?e indicates that this is an equation label, the different nil elements indicate to use the default values for equations. The `1' as the fifth element indicates that the context of the label definition should be the 1st argument of the macro.

Here is again how this would look in the customization buffer:

Reftex Label Alist: [Hide]
[INS] [DEL] Package or Detailed   : [Value Menu] Detailed:
            Environment or \macro : [Value Menu] String: \quickeq{}
            Type specification    : [Value Menu] Char  : e
            Label prefix string   : [Value Menu] Default
            Label reference format: [Value Menu] Default
            Context method        : [Value Menu] Macro arg nr: 1
            Magic words:
              [INS]
            [ ] Make TOC entry    : [Value Menu] No entry

3.4.3 Figure Wrapping Macro

Suppose you want to make figures not directly with the figure environment, but with a macro like

\newcommand{\myfig}[5][tbp]{%
  \begin{figure}[#1]
    \epsimp[#5]{#2}
    \caption{#3}
    \label{#4}
  \end{figure}}

which would be called like

\myfig[htp]{filename}{caption text}{label}{1}

Now we need to tell RefTeX that the 4th argument of the \myfig macro is itself a figure label, and where to find the context.

(setq reftex-label-alist
      '(("\\myfig[]{}{}{*}{}" ?f nil nil 3)))

The empty pairs of brackets indicate the different arguments of the \myfig macro. The `*' marks the label argument. ?f indicates that this is a figure label which will be listed together with labels from normal figure environments. The nil entries for prefix and reference format mean to use the defaults for figure labels. The `3' for the context method means to grab the 3rd macro argument - the caption.

As a side effect of this configuration, reftex-label will now insert the required naked label (without the \label macro) when point is directly after the opening parenthesis of a \myfig macro argument.

Again, here the configuration in the customization buffer:

[INS] [DEL] Package or Detailed   : [Value Menu] Detailed:
            Environment or \macro : [Value Menu] String: \myfig[]{}{}{*}{}
            Type specification    : [Value Menu] Char  : f 
            Label prefix string   : [Value Menu] Default
            Label reference format: [Value Menu] Default
            Context method        : [Value Menu] Macro arg nr: 3
            Magic words:
              [INS]
            [ ] Make TOC entry    : [Value Menu] No entry

3.4.4 Adding Magic Words

Sometimes you don't want to define a new label environment or macro, but just change the information associated with a label category. Maybe you want to add some magic words, for another language. Changing only the information associated with a label category is done by giving nil for the environment name and then specify the items you want to define. Here is an example which adds German magic words to all predefined label categories.

(setq reftex-label-alist
  '((nil ?s nil nil nil ("Kapitel" "Kap." "Abschnitt" "Teil"))
    (nil ?e nil nil nil ("Gleichung" "Gl."))
    (nil ?t nil nil nil ("Tabelle"))
    (nil ?f nil nil nil ("Figur" "Abbildung" "Abb."))
    (nil ?n nil nil nil ("Anmerkung" "Anm."))
    (nil ?i nil nil nil ("Punkt"))))

3.4.5 Using \eqref

Another case where one only wants to change the information associated with the label category is to change the macro which is used for referencing the label. When working with the AMS-LaTeX stuff, you might prefer \eqref for doing equation references. Here is how to do this:

(setq reftex-label-alist '((nil ?e nil "~\\eqref{%s}" nil nil)))

RefTeX has also a predefined symbol for this special purpose. The following is equivalent to the line above.

(setq reftex-label-alist '(AMSTeX))

Note that this is automatically done by the `amsmath.el' style file of AUCTeX (see section 6.8.2 Style Files) - so if you use AUCTeX, this configuration will not be necessary.

3.4.6 Non-standard Environments

Some LaTeX packages define environment-like structures without using the standard `\begin..\end' structure. RefTeX cannot parse these directly, but you can write your own special-purpose parser and use it instead of the name of an environment in an entry for reftex-label-alist. The function should check if point is currently in the special environment it was written to detect. If so, it must return a buffer position indicating the start of this environment. The return value must be nil on failure to detect the environment. The function is called with one argument bound. If non-nil, bound is a boundary for backwards searches which should be observed. We will discuss two examples.

Some people define abbreviations for environments, like \be for \begin{equation}, and \ee for \end{equation}. The parser function would have to search backward for these macros. When the first match is \ee, point is not in this environment. When the first match is \be, point is in this environment and the function must return the beginning of the match. To avoid scanning too far, we can also look for empty lines which cannot occur inside an equation environment. Here is the setup:

;; Setup entry in reftex-label-alist, using all defaults for equations
(setq reftex-label-alist '((detect-be-ee ?e nil nil nil nil)))

(defun detect-be-ee (bound)
  ;; Search backward for the macros or an empty line
  (if (re-search-backward 
       "\\(^[ \t]*\n\\|\\\\ee\\>\\)\\|\\(\\\\be\\>\\)" bound t)
      (if (match-beginning 2)
          (match-beginning 2)  ; Return start of environment
        nil)                   ; Return nil because env is closed
    nil))                      ; Return nil for not found

A more complex example is the `linguex.sty' package which defines list macros `\ex.', `\a.', `\b.' etc. for lists which are terminated by `\z.' or by an empty line.

\ex.  \label{ex:12} Some text in an exotic language ...
      \a. \label{ex:13} more stuff
      \b. \label{ex:14} still more stuff
          \a. List on a deeper level
          \b. Another item
          \b. and the third one
      \z.
      \b. Third item on this level.

... text after the empty line terminating all lists

The difficulty is that the `\a.' lists can nest and that an empty line terminates all list levels in one go. So we have to count nesting levels between `\a.' and `\z.'. Here is the implementation for RefTeX.

(setq reftex-label-alist
      '((detect-linguex ?x "ex:" "~\\ref{%s}" nil ("Example" "Ex."))))

(defun detect-linguex (bound)
  (let ((cnt 0))
    (catch 'exit
      (while 
          ;; Search backward for all possible delimiters
          (re-search-backward
           (concat "\\(^[ \t]*\n\\)\\|\\(\\\\z\\.\\)\\|"
                   "\\(\\ex[ig]?\\.\\)\\|\\(\\\\a\\.\\)")
           nil t)
        ;; Check which delimiter was matched.
        (cond 
         ((match-beginning 1)
          ;; empty line terminates all - return nil
          (throw 'exit nil))
         ((match-beginning 2)
          ;; \z. terminates one list level - decrease nesting count
          (decf cnt))
         ((match-beginning 3)
          ;; \ex. : return match unless there was a \z. on this level
          (throw 'exit (if (>= cnt 0) (match-beginning 3) nil)))
         ((match-beginning 4)
          ;; \a. : return match when on level 0, otherwise
          ;;       increment nesting count
          (if (>= cnt 0)
              (throw 'exit (match-beginning 4))
            (incf cnt))))))))

3.4.7 Putting it all together

When you have to put several entries into reftex-label-alist, just put them after each other in a list, or create that many templates in the customization buffer. Here is a lisp example which uses several of the entries described above:

(setq reftex-label-alist
  '(("axiom"   ?a "ax:"  "~\\ref{%s}" nil ("axiom"   "ax.") -2)
    ("theorem" ?h "thr:" "~\\ref{%s}" t   ("theorem" "theor." "th.") -3)
    ("\\quickeq{}" ?e nil nil 1 nil)
    AMSTeX
    ("\\myfig[]{}{}{*}{}" ?f nil nil 3)
    (detect-linguex ?x "ex:" "~\\ref{%s}" nil ("Example" "Ex."))))

3.5 Reference Info

When point is idle for more than reftex-idle-time seconds on the argument of a \ref macro, the echo area will display some information about the label referenced there. Note that the information is only displayed if the echo area is not occupied by a different message.

RefTeX can also display the label definition corresponding to a \ref macro, or all reference locations corresponding to a \label macro. See section 6. Viewing Cross--References, for more information.

3.6 xr: Cross-Document References

The LaTeX package xr makes it possible to create references to labels defined in external documents. The preamble of a document using xr will contain something like this:

\usepackage{xr}
\externaldocument[V1-]{volume1}
\externaldocument[V3-]{volume3}

and we can make references to any labels defined in these external documents by using the prefixes `V1-' and `V3-', respectively.

RefTeX can be used to create such references as well. Start the referencing process normally, by pressing C-c ). Select a label type if necessary. When you see the label selection buffer, pressing x will switch to the label selection buffer of one of the external documents. You may then select a label as before and RefTeX will insert it along with the required prefix.

For this kind of inter-document cross-references, saving of parsing information and the use of multiple selection buffers can mean a large speed-up (see section 6.7 Optimizations).

3.7 varioref: Variable Page References

3.8 fancyref: Fancy Cross References

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