# Purpose of SLACcitation field

I'm working with BibTeX generated by InspireHEP, which includes a SLACcitation field (which looks to be REVTeX specific).

When I render this MWE, the SLACcitation does not show up anywhere. Are there styles that do use the field? Is it required in REVTeX? Is there documentation on its use?

\documentclass{revtex4-1}
\usepackage[utf8]{inputenc}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@article{Purrer:2015tud,
author         = "Pürrer, Michael",
title          = "{Frequency domain reduced order model of aligned-spin
effective-one-body waveforms with generic mass-ratios and
spins}",
journal        = "Phys. Rev.",
volume         = "D93",
year           = "2016",
number         = "6",
pages          = "064041",
doi            = "10.1103/PhysRevD.93.064041",
eprint         = "1512.02248",
archivePrefix  = "arXiv",
primaryClass   = "gr-qc",
SLACcitation   = "%%CITATION = ARXIV:1512.02248;%%"
}
\end{filecontents}

\begin{document}
\nocite{*}
\bibliography{\jobname}
\end{document}


Edit: what's below was based on a syntax error of mine; you can safely ignore what's below but I'm leaving it in so the comments below make sense.

On a side note, when I change the quotes around the fields to braces, they are accepted for all but the SLACcitation field; it looks like the percentage signs are interpreted differently inside quotes vs braces. Yet Tame the BeaST says

Values (i.e. right hand sides of each assignment) can be either between curly braces or between double quotes. The main difference is that you can write double quotes in the first case, and not in the second case.

Are there more differences between quotes and braces?

• On my installation only REVTeX styles print the field. I found slac.stanford.edu/spires/hep/refs/bibstyles.shtml – moewe Dec 30 '18 at 18:59
• At least in my tests I could not find a difference between "..." and {...} for SLACcitation. Did you get different behaviour? If so, how did the behaviour differ? As far as I can see the information is just written as is in a new line to the .bbl file, but since it starts with %% it is ignored in the output. I guess it is supposed to be some kind of metadata for citation analysis. – moewe Dec 30 '18 at 19:05
• – moewe Dec 30 '18 at 19:09
• I would never have found that -- thanks. So, this applies to both bibtex and biblatex. I've tried getting the MWE at overleaf.com/4345765536fmvztnsjxqtx to render the SLACcitation but none of the styles I tried were found at Overleaf. Am I doing it wrong? – retorquere Dec 30 '18 at 19:38
• If you want an authoritative answer I guess you should contact inspirehep.net why they export that field. Their email is feedback@inspirehep.net, they also have a twitter account (twitter.com/inspirehep) if you have an account and like that sort of thing, but I'm not sure if they respond there. – moewe Dec 30 '18 at 21:37

On my system a search for SLACcitation in \$TEXMF/bibtex/bst/ only turns up the REVTeX styles. On CTAN there is also chetref.bst, but the code for SLACcitation there is commented out. SPIRES: BibTeX Style Files lists a few other styles.

The REVTeX 4.1 announcement mentions SLACcitation in association with arXiv support, but does not explain the use of the field further.

SPIRES: BibTeX Style Files and LaTeX Output and SPIRES citation gathering (Wayback machine snapshot from 2004-10-26) as well as BibTeX from SPIRES (Wayback machine snapshot from 2004-12-24) suggest that SLACcitation contains some kind of citation metadata that is/was used by SPIRES probably to track citations. (Cf. also http://www.inr.ac.ru/~fedor/jabref/spires2.3.patch)

All styles that support the field write it in a line of its own, so that an entry in the .bbl would look like (from LaTeX Output and SPIRES citation gathering (Wayback machine snapshot from 2004-10-26))

\bibitem{Morningstar:1997ff}
C.J.~Morningstar and M.~Peardon,
%Efficient glueball simulations on anisotropic lattices,"
Phys. Rev. {\bf D56}, 4043 (1997)
hep-lat/9704011.
%%CITATION = PHRVA,D56,4043;%%


Due to the %% in front of the CITATION LaTeX would ignore the rest of the line and the SLACcitation field would produce no output in the bibliography. The tag is only visible in the source code. Indeed LaTeX Output and SPIRES citation gathering (Wayback machine snapshot from 2004-10-26) says

Our program looks for the %%CITATION tag in your .tex file (which, of course, will not show up in the printed copy of your paper).

but does not go on to explain what exactly the program does. http://inspirehep.net/info/faq/references_citations also suggests that

As usual SLACcitation will be ignored by all styles where the field has not been declared. It is also ignored by (standard) biblatex (and all contributed styles I know), but if it were read by biblatex the %% would produce errors if the field was not read in verbatim mode.

Since there is no further documentation of the field and no other mentions on the web besides the meagre few sites mentioned above and a great many exported .bib entries, I doubt this field is very important, let alone required for REVTeX. INSPIRE References and Citations: How can I ensure my references are fully extracted? refers to formats that output the %%CITATION metadata, but it is not clear to me from the rest of this site that the tag is a requirement.

SPIRES (INSPIRE's predecessor) used to extract references for papers from LaTeX sources. Putting a %%CITATION = ... comment in a reference was a clever trick to make it easy to identify the cited record without it affecting the typeset paper. That's why it appeared in (and still does on INSPIRE) in the LaTeX export formats. For people who were using BibTeX to handle their bibliography instead of getting straight bibitems from SPIRES, some additional trick was needed to have bibtex output the proper comment: the SLACcitation field was added to the BibTeX export format, so that a BibTeX style could just pick up that field and put it somewhere in the reference to have it recognized properly by SPIRES.
As authors needed to do many things to make it work properly and parsing TeX is hard, this method of recognizing references was abandoned on INSPIRE. Instead, references are now extracted from the PDF and citations identified by searching our records for potential matches, based on identifiers (DOI, arXiv ID, etc.) and publication information (journal title, volume, pages, etc.). We also try to match the citation key (which appears in the PDF as a named destination when hyperref is used), as the keys we expose in the LaTeX/BibTeX export formats are unique identifiers for papers on INSPIRE. The %%CITATION = ... comment and assorted BibTeX field have survived until now, but will be removed in an upcoming update of INSPIRE as they are no longer needed.
• %%CITATION = was used to identify citations without affecting the typeset output
• SLACcitation was used to produce %%CITATION = from .bib files
• nowadays %%CITATION and SLACcitation are not used any more