Citations in org-mode: Org-cite and Citar

Summary

First, I’ll outline the broadest components to producing files in org-mode with a citation system (e.g. org-cite, org-ref). Then I’ll introduce org-cite and the differences between its bibtex, csl, and basic export processors. Then, I will walk through my configuration for org-cite and citar (formerly bibtex-actions). You can see a gist of all the code present in this post here.

My goal is to plot the landscape, preparing you to understand other available sources which are more suited for a user already familiar with the landscape.

I recommend the following reading for more information regarding how org-cite works:

Citation handling (The Org Manual)
The first source you should visit should almost always be the manual (available within Emacs via info, i.e. M-x info). It covers the fundamentals to understanding how to use org-cite. Isn’t well documented currently, but that will change in the future.
Org-cite guide by tecosaur
I’ll be referencing this frequently, for good reason.

What are citation systems?

There are roughly three moving parts to citation management.

1. The tool that produces the bibliography file.
A bibliography file is where information regarding sources are stored. This almost always comes in the form of a .bib file; usually one is sufficient. There are various ways to create these files. Though you can manually create your own .bib files, the most common way is exporting a Zotero library (see Zotero).
2. The text processor.
This is the software the user (you) directly writes in. In our case, it’s Emacs!
3. The “layer” from text to product.
This is the code that lies in between your plain text writing and an output file (e.g. PDF). Sometimes this is identical to the text processor—in our case it isn’t. For instance, Microsoft Word is both a text editor and the producer of an output file, such as a PDF or a .docx.

org-cite lies closer to (3) because it is responsible for exporting citations, whereas citar is closer to (2) because it is an interface for inserting citations into the buffer. A software like Zotero is responsible for (1).

Org-cite

In around July of 2021, org-cite was publicly released. org-cite a library packaged with org-mode that processes org citations (e.g. [cite:@wittgensteinTractatusLogicoPhilosophicus2021]). To those not familiar with another citation workflow (e.g. biblatex in LaTeX), it is quite daunting to leap into citations in Emacs. This was certainly the case for me: I leapt into org-mode citation integration with Zotero and LaTeX with no experience in org, Zotero, or LaTeX! Nonetheless, org-cite is quite simple once laid out. After reading this post or section, I recommend taking a look at tecosaur’s fabulous guide to using org-cite. His explanation of the citation styles of org-cite and their variants is particularly useful.

Understanding org-cite export processors

The most crucial concept to org-cite are “export processors.” Take a look at the following passage from the documentation for org-cite-export-processors:

When non-nil, the value is an association list between export back-ends and
citation export processors:

(BACK-END . PROCESSOR)

where BACK-END is the name of an export back-end or t, and PROCESSOR is a
triplet following the pattern

(NAME BIBLIOGRAPHY-STYLE CITATION-STYLE)

There, NAME is the name of a registered citation processor providing export
functionality, as a symbol.  BIBLIOGRAPHY-STYLE (respectively CITATION-STYLE)
is the desired default style to use when printing a bibliography (respectively
exporting a citation), as a string or nil.  Both BIBLIOGRAPHY-STYLE and
CITATION-STYLE are optional.  NAME is mandatory.


What this suggests is that different combinations of “processors,” “bibliography styles,” and “citation styles” can be configured to work with different org-export backends. Presently, there are three processors available: basic, csl, natbib, and bibtex. Though org-cite citations will always follow the same format, the output text that is exported will change depending on the processor used. I will go over these differences now, focusing primarily on the bibtex and csl backends1.

The bibtex processor can only be used with the latex backend. Using this processor exports citations using the BibLaTex LaTeX package. That means that [cite:@bradleyAppearanceRealityMetaphysical2011 82–5;] will export into a LaTeX command like \cite[82–5]{bradleyAppearanceRealityMetaphysical2011}. Compiling the org exported LaTeX file will in turn produce a PDF whose citations are handled by biblatex. The end citation style will be determined by the provided package options (e.g. style=mla-new). Read the biblatex documentation for more information (namely, section 3.1.1 in the February 2, 2022 version of the manual).

The natbib processor unsurprisingly uses the natbib LaTeX package. biblatex is slowly growing to replace the older natbib package, though some users may circumstantially be limited to natbib​—you can read more about the differences between natbib and biblatex here. I have not personally used the natbib, but I suspect its usage is similar if not identical to the bibtex processor.

The csl processor will use CSL to export citations. Citation Style Language (CSL) is a language used to instruct the formatting of citations and bibliographies; citation styles are provided by .csl files. Most importantly, CSL is intended to be a universal standard for citation formatting. Accordingly, .csl supports essentially every output format.

In sum:

flowchart LR A((Plain-text)) --- B{Org-export} B ===> C B ===>D B ===> E subgraph CSL Processor C{{HTML, MD, ODT, plain-text, etc.}} D[LaTeX] D -.->|Compile with citations as rendered text| F(PDF) end subgraph Bibtex and Natbib processor E[LaTeX] E -.->|Compile with citations as LaTeX commands|G(PDF) end

Which processor should I use?

The most common confusion comes from realizing that CSL can also export to LaTeX. So, when exporting to LaTeX: should you use the csl or bibtex/natbib processor? The difference lies in whether or not you want to rely on the biblatex package to manage exports.

The important difference is that csl exports to rendered text. Rendered text is text whose end formatting will match that of org’s, e.g. italic text in org-mode will become wrapped in, say, \emph{} in LaTeX. So, for instance, if I export [cite:@bradleyAppearanceRealityMetaphysical2011 82–5;] into a LaTeX file using the csl processor using a CSL file for the Modern Language Association (MLA) citation style, I will see the following in-text citation in the LaTeX file as: (Bradley 82–85)​—if anything needed to be bold, italicized, etc., then that would be wrapped in the appropriate LaTeX command. Contrast that with the LaTeX command in the paragraphs above.

So when it comes to exporting to LaTeX, when wouldn’t rendered text be enough? If you want the most basic functionality, i.e. “Seeing in-text citations and bibliographies in my documents is enough,” then CSL will always cover you. However, if you want access to the more complex or nuanced facilities of biblatex, use the bibtex processor instead. biblatex use cases include (i) using obscure or uncommon field and entry types and (ii) wanting “automation” in the citation variant. By (ii) I mean that biblatex handles the variant whereas you must manually list the variant in the org-cite citation when using CSL (see the above link to tecosaur’s guide).

I will give an example. Basic MLA in-text citations following a (AUTHOR PAGE) format. However, closely following MLA means that subsequent in-text citations from the same source should have a (PAGE) format. Using the csl processor, without specifying a style or variant in the org-cite citation, will always output the former formatting as rendered text; as r/bdarcus explains in his comment, CSL focuses on higher-level commands in order to be agnostic of output format. On the other hand, org-cite will, by default, leverage the \autocite command (see org-cite-biblatex-styles). This tells biblatex to change the variant when appropriate. This is an immensely powerful upside to using the bibtex processor—though it is minor in this particular case, this demonstrates the advantages of the biblatex package. You can read more about the differences between CSL and biblatex in this thorough StackExchange explanation. Of course, however, biblatex is only available when exporting to LaTeX, whereas CSL can be used to export into any format (e.g. HTML, Markdown, ODT, plain-text).

In sum, use the bibtex processor when you are exporting to LaTeX and only LaTeX and

• want automatic selection of citation variants
• or have rare field or entry types in your .bib file.

Otherwise, use the csl processor2 (assuming you have a .csl file for your desired citation style).

Finally, it should be noted that the csl and bibtex processors use different locators in citations. As explained in tecosaur’s guide, the csl processor uses locators like bk. and vol., so citations may look like [cite/noauthor:See@mollisonNietzscheContraStoicism2018 pp. 28–9;@priestWhyItIrrational2001 pp. 14;]​—CSL processes these locators. On the other hand, a citation key’s suffix is directly passed as an option to BibLaTeX commands, so an equivalent to the above would be [cite/noauthor:See@mollisonNietzscheContraStoicism2018 28–9;@priestWhyItIrrational2001 14;], which doesn’t have CSL locators.

Configuration

Luckily, the difficulty in org-cite is only conceptually: configuring it is incredibly straightforward. There are two main variables that affect functionality. The first is crucial, and the second is useful to be aware of:

1. org-cite-global-bibliography
2. org-cite-export-processors

org-cite-global-bibliography is the bare minimum to getting org-cite ready to work. This should be a list of bibliography file (.bib) paths. I have mine set to a list whose single element is a file that Zotero exports:

:custom
;; Actually, I set this value to kb/bib-files', which is a list of file paths.
;; I set that as the value of any variable that requires bibliography files,
;; such as citar', as you'll see below.
(org-cite-global-bibliography
'("/home/krisbalintona/Documents/org-database/roam/references/master-lib.bib"))


Alternatively, you can use the org-mode #+BIBLIOGRAPHY: keyword to set this value per-file; it’s value should be a file path.

org-cite-export-processors is useful as a means to tweak how you’d like org-cite to export citations. You can also set a file-local value using the #+CITE_EXPORT file keyword (e.g. #+CITE_EXPORT: csl chicago-author-date.csl); see this section in tecosaur’s guide for an example of how to set the processor, bibliography style, and citation style with this keyword. For a given backend3, you can choose how org-cite exports it. For instance, here is mine:

:custom
(org-cite-export-processors
'((md . (csl "chicago-fullnote-bibliography.csl"))   ; Footnote reliant
(latex . biblatex)                                 ; For humanities
(odt . (csl "chicago-fullnote-bibliography.csl"))  ; Footnote reliant
(t . (csl "modern-language-association.csl"))      ; Fallback
))


As you can see, I have CSL be the default in every case aside from LaTeX. The styles can either be a file path or a file name in org-cite-csl-styles-dir​—see Zotero for how to easily acquire CSL files.4 (I use LaTeX strictly for my academic papers, so I really enjoy biblatex’s features.)

I also choose to customize faces—I prefer the green faces that org-ref uses:5

:custom-face
;; Have citation link faces look closer to as they were for org-ref'
(org-cite ((t (:foreground "DarkSeaGreen4"))))
(org-cite-key ((t (:foreground "forest green" :slant italic))))


Usage

Using org-cite is incredibly simple:

1. org-cite-insert to insert citations in org files, and
2. #+PRINT_BIBLIOGRAPHY: within a document to mark where the bibliography/references/works cited should be.6

Citar

Using org-cite is really simple. But many users will find the interface… too bare. Citar is, roughly, the foremost attempt to provide a pleasing frontend to org-cite. It adds the citar citation-insert processor. The following is the minimum to start using citar:

(use-package citar
;; The :straight' keyword is not necessary. However, I do this to set a value
;; for the :includes' keyword. This keyword tells use-package that those
;; package(s) are provided by this package, and not to search for them on
;; Melpa for download. Alternatively, you can set the :straight' keyword to
;; nil in those package(s) use-package declaration.
:straight (citar :type git :host github :repo "emacs-citar/citar" :includes (citar-org))
:custom
;; A list of bib files. A good idea would be having its value be identical to
;; that of org-cite-global-bibliography'. For me, I have all my bib file(s)
;; as a list of strings in kb/bib-files'.
(citar-bibliography kb/bib-files))

;; Use citar' with org-cite'
(use-package citar-org
:after oc
:custom
(org-cite-insert-processor 'citar)
(org-cite-follow-processor 'citar)
(org-cite-activate-processor 'citar))


You can then set keybinds for common citar commands. For example, in the :general use-package keyword:7

:general
(:keymaps 'org-mode-map
:prefix "C-c b"
"b" '(citar-insert-citation :wk "Insert citation")
"r" '(citar-insert-reference :wk "Insert reference")
"o" '(citar-open-notes :wk "Open note"))


If you use embark and org-roam you can also set these variables:

:custom
(citar-notes-paths (list kb/roam-dir)) ; List of directories for reference nodes
(citar-open-note-function 'orb-citar-edit-note) ; Open notes in org-roam'
(citar-at-point-function 'embark-act)           ; Use embark'


Capturing

If you use org-roam, then the following is how you select bibliographic source and create an org-roam node from it. All credit goes to Jethro Kuan, the creator of org-roam, though I’ve made a few of my own customizations:8

;; Create a new node from a bibliographic source. taken from
;; https://jethrokuan.github.io/org-roam-guide/
(defun kb/org-roam-node-from-cite (keys-entries)
(interactive (list (citar-select-ref :multiple nil :rebuild-cache t)))
(let ((title (citar--format-entry-no-widths (cdr keys-entries)
"${author editor}${date urldate} :: ${title}"))) (org-roam-capture- :templates '(("r" "reference" plain "%?" :if-new (file+head "references/${citekey}.org"
":properties:
:roam_refs: [cite:@${citekey}] :end: #+title:${title}
#+filetags: %(kb/insert-lit-category)\n")
:immediate-finish t
:unnarrowed t))
:info (list :citekey (car keys-entries))
:node (org-roam-node-create :title title)
:props '(:finalize find-file))))


I add it to an accessible keybinding:9

:general
(kb/note-keys                           ; global-map
"C" '(kb/org-roam-node-from-cite :wk "Citar-capture"))


Advising citar-org-update-pre-suffix

A useful command is citar-org-update-pre-suffix. This command sets the prefix and suffix of a citation key (a single citation can have multiple keys). This is notable since a citation’s suffix is where you provide a locator (e.g. a page number). The command is bound to M-p when the point is on a citation key.

Before advising citar-org-update-pre-suffix, I first advise org-cite-insert such that citar-org-update-pre-suffix is run immediately after inserting a citation:

;; Run citar-org-update-pre-suffix' after inserting a citation to immediately
;; set its prefix and suffix
(save-excursion
(left-char) ; First move point inside citation
(citar-org-update-pre-suffix))))


A limitation with this code is that this only calls citar-org-update-pre-suffix on the last citation key, which is fine when only one key is inserted at once, and not when multiple are inserted. (Though, citar-org-update-pre-suffix can still be called manually on the other citation keys afterward.)

Additionally, I override citar-org-update-pre-suffix with my own version which adds the following functionality:

1. Temporarily enable typo-mode.10
2. Avoid manually inserting a separating space in the suffix.
(defun kb/citar-org-update-pre-suffix ()
"Change the pre/suffix text of the reference at point.

My version also adds a space in the suffix so I don't always have
(interactive)

;; Enable typo' typographic character cycling in minibuffer. Particularly
;; useful in adding en- and em-dashes in citation suffixes (e.g. for page
;; ranges)
(when (featurep 'typo)
(add-hook 'minibuffer-mode-hook 'typo-mode)) ; Enable dashes

(let* ((datum (org-element-context))
(datum-type (org-element-type datum))
(ref (if (eq datum-type 'citation-reference) datum
(error "Not on a citation reference")))
(key (org-element-property :key ref))
;; TODO handle space delimiter elegantly.
(pre (read-string "Prefix text: " (org-element-property :prefix ref)))
(post (read-string "Suffix text: " (org-element-property :suffix ref))))

;; Change post to automatically have one space prior to any user-inputted
;; suffix
(setq post
(if (string= (replace-regexp-in-string "\s-*" "" post) "")
""         ; If there is nothing of substance (e.g. an empty string)
(replace-regexp-in-string "^[\s-]*" " " post))) ; Only begin with one space

(setf (buffer-substring (org-element-property :begin ref)
(org-element-property :end ref))
(org-element-interpret-data
(citation-reference
(:key ,key :prefix ,pre :suffix ,post)))))

;; Remove hook if it was added earlier
(remove-hook 'minibuffer-mode-hook 'typo-mode))


One can also add this command to citar-citation-map.11

Aesthetics

Finally, we can change the way the citar interface appears. The most relevant variables are citar-templates and citar-symbols. Below is my configuration for these variables. Notably, my definition for citar-symbols utilizes all-the-icons icons to fancify the candidates (all-the-icons must be installed in order to have the faces below available):

:custom
(citar-templates
'((main . "${author editor:30}${date year issued:4}    ${title:110}") (suffix . "${=type=:20}    ${tags keywords keywords:*}") (preview . "${author editor} (${year issued date})${title}, ${journal journaltitle publisher container-title collection-title}.\n") (note . "#+title: Notes on${author editor}, \${title}") ; For new notes
))
;; Configuring all-the-icons. From
;; https://github.com/bdarcus/citar#rich-ui
(citar-symbols
((file ,(all-the-icons-faicon "file-o" :face 'all-the-icons-green :v-adjust -0.1) .
,(all-the-icons-faicon "file-o" :face 'kb/citar-icon-dim :v-adjust -0.1) )
(note ,(all-the-icons-material "speaker_notes" :face 'all-the-icons-blue :v-adjust -0.3) .
,(all-the-icons-material "speaker_notes" :face 'kb/citar-icon-dim :v-adjust -0.3))
(citar-symbol-separator "  ")
:init
;; Here we define a face to dim non 'active' icons, but preserve alignment.
;; Change to your own theme's background(s)
(defface kb/citar-icon-dim
;; Change these colors to match your theme. Using something like
;; face-attribute' to get the value of a particular attribute of a face might
;; be more convenient.
'((((background dark)) :foreground "#212428")
(((background light)) :foreground "#f0f0f0"))
"Face for having icons' color be identical to the theme
background when \"not shown\".")


Here’s the end-result:

Other interesting packages

Zotero

Zotero isn’t an Emacs package, but it is crucial to most users’ workflow, so it deserves attention. Zotero makes gathering, storing, and exporting bibliographic data infinitely easier. For instance, an ISBN or DOI of a source is all that is necessary for an entry’s fields to be populated. There are two things to note about my setup:

1. I install the BetterBibLaTex add-on (see its features in the official documentation page. Its main benefits include unique citation key generation and exporting facilities),
2. and export my library using the BetterBibLaTeX format. I also tick the “Keep Updated” option; this continually updates the .bib file as I make changes to my library. I then point org-cite-global-bibliography and citar-bibliography to this file.

Additionally, for over a year now, I’ve been using Zotero’s own PDF viewer and annotator. Until recently, this feature had only been available in Zotero Beta, but it is now merged onto the main branch. Though it isn’t powerful, it gets the job done for me, and the convenience is what sells it.

Finally, a very handy tip is to use the CSL files that Zotero already provides (credit to this section of tecosaur’s guide). The CSL files (which provide citation styles) are located in ZOTERO_DIR/styles/. You can set org-cite-csl-styles-dir to this path:

:custom
(org-cite-csl-styles-dir
(expand-file-name "~/Documents/Zotero/styles/"))


Embark

Embark provides menus (essentially keymaps) based on “context,” that is, the type of thing the point is on. As a result, embark has immense potential. Citar is built to exploit embark without requiring it—for instance, see citar-citation-map.

Org-roam-bibtex

Org-roam-bibtex integrates org-roam with citation systems, such as org-cite. This packages allows org-roam to recognize particular nodes as bibliographic (i.e. associated with a particular .bib entry).

Additionally, as as citar’s author, u/bdarcus, shares here, there is work being done on citar’s end to more tightly integrate org-roam with citar, in the form of citar-org-roam.

Citar-capf

Citar-capf provides a complation-at-point-function12 for citations. However, if you’re reading this in the future, there’s a likely chance that this commit would have been merged. The commit merges citar-capf with citar.

Org-ref

Org-ref has historically been the dominant citation system for org-mode. I elect to use org-cite instead because (i) it comes with org-mode, meaning there is one less conceptual- and configuration-layer to navigate, (ii) Moreover, org-ref uses a format that follows org conventions less closely, and (iii) I have read that is arguably more robust and future-proof. Nevertheless, some users still prefer it.

Changelog

• [2022-06-15 Wed]
• [2022-06-19 Sun]
• Change processor explanations to include the natbib processor.
• Change processor explanations to recognize the difference between plain-text and rendered text.

Writing papers in org-mode series

1. Citations in org-mode: Org-cite and Citar (this post!)
2. Org and LaTeX integration (coming soon!)
3. Org-mode niceties (coming soon!)

1. The basic processor provides bare functionality and should never be preferred over the alternative, if possible. ↩︎

2. See Configuration↩︎

3. This is an org-export backend. This means that, for instance, md refers to the org-export md backend as well as any other derived backends. Read the documentation for org-export-define-derived-backend↩︎

4. Notice that a citation style is required for the csl processor, and not for the bibtex processor. ↩︎

5. Be aware that I use use-package’s :custom-face keyword to redefine these two faces. One can just as easily use the built-in defface of set-face-attribute↩︎

6. Also see this section of tecosaur’s guide↩︎

7. You can also just use the built-in define-key↩︎

8. This assumes that you have org-roam-bibtex installed and enabled. See Org-roam-bibtex↩︎

9. kb/note-keys is my own general.el leader key. I’ve mapped its prefix to C-c n↩︎

10. I prefer directly inserting curly quotes, em-dashes, and en-dashes into my buffers. I enable typo-mode` here so that typing page ranges properly inserts en-dashes. ↩︎

11. See Embark↩︎