Pfthb

I am trying to change the way that labels are generated. Some of it I already got working (only at maximum two authors, only last two digits of the year), but one thing does not seem to work, which is putting an ampersand between the authors if there are at least two.
In the manual on page 205 it is explained, that one can use special characters without escaping them as literals or padding, but what about the namessep field?

In the MWE I used 'X' in the place where an '&' should be placed, but I do not know how to do it.
I suspect, that since it is converted into the .bcf file, which is XML, that the ampersand makes troubles there, so is this a bug?

Here is a MWE:

documentclassarticle
usepackage[utf8]inputenc
usepackage[english]babel
usepackagecsquotes
usepackagefilecontents

beginfilecontents*references.bib
@articleeinstein,
 author = "Albert Einstein and Second Author",
 title = "Zur Elektrodynamik bewegter K"orper. (German)
 [On the electrodynamics of moving bodies]",
 journal = "Annalen der Physik",
 volume = "322",
 number = "10",
 pages = "891--921",
 year = "1905",
 DOI = "http://dx.doi.org/10.1002/andp.19053221004",
 keywords = "physics"


@bookdirac,
 title=The Principles of Quantum Mechanics,
 author=Paul Adrien Maurice Dirac,
 isbn=9780198520115,
 series=International series of monographs on physics,
 year=1981,
 publisher=Clarendon Press,
 keywords = physics


@booklatexcompanion,
 author = "Michel Goossens and Frank Mittelbach and Alexander Samarin",
 title = "The LaTeX Companion",
 year = "1993",
 publisher = "Addison-Wesley",
 address = "Reading, Massachusetts",
 keywords = "latex"

endfilecontents*

usepackage[
backend=biber,
style=alphabetic,
citestyle=alphabetic,
maxcitenames=2,
mincitenames=2,
giveninits=true,
isbn=false,
]biblatex

renewcommand*labelalphaothers$^+$

DeclareLabelalphaTemplate
 labelelement
 field[final]shorthand
 fieldlabel
 field[names=2, namessep=addspaceXaddspace]labelname
 
 labelelement
 literaladdspace
 
 labelelement
 field[strside=right,strwidth=2]year
 


addbibresourcereferences.bib

begindocument
sectionFirst section

Items that are cited: textitThe LaTeX Companion book citelatexcompanion, The Einstein's journal paper citeeinstein and the Dirac's book citedirac are physics related items. Next, a citation about textitThe LaTeX Companion book citelatexcompanion.

medskip

printbibliography
enddocument

Render of MWE:

Hide the ampersand in a command (& is not good enough because the command name contains an ampersand, which still throws the XML off) and use detokenize to make sure the macro does not get expanded when it is written to the .bcf.

detokenize can often be a cheap work-around if biblatex options that may contain printable data explode. Often that happens because the value of the option needs to be written to the .bcf file, so Biber can consume its value. LaTeX usually performs full expansion when text is written to a file, so things may go wrong if the desired value is not expandable or (as in this case) expands to problematic text. detokenize stops this unwanted expansion. When the value is then picked up from the .bbl file, the tokens will be interpreted as usual and the output will be as expected.

The quoted passage on page 205 of the manual only applies to padchar and literal, the value of namessep needs escaping for special characters in both LaTeX and XML.

documentclassarticle
usepackage[utf8]inputenc
usepackage[english]babel
usepackagecsquotes

usepackage[backend=biber,style=alphabetic,maxcitenames=2,mincitenames=2,giveninits=true,isbn=false,]biblatex

renewcommand*labelalphaotherstextsuperscript+
newcommand*ampersand&

DeclareLabelalphaTemplate
 labelelement
 field[final]shorthand
 fieldlabel
 field[names=2, namessep=detokenizeaddspaceampersandspace]labelname
 
 labelelement
 literaladdspace
 
 labelelement
 field[strside=right,strwidth=2]year
 


addbibresourcebiblatex-examples.bib

begindocument
citecompanion,sigfridsson,worman

printbibliography
enddocument

I'm not a big fan of abusing alphabetic to obtain what is essentially a full-blown author-year style with square brackets and the labels in the bibliography, but because it is a bit tricky to get only the last two digits of the year and retain uniqueness features I can't offer a simple implementation of the exact same style with style=authoryear, but

documentclassarticle
usepackage[utf8]inputenc
usepackage[english]babel
usepackagecsquotes

usepackage[backend=biber,style=ext-authoryear,
 introcite=label,
 autocite=inline,
 maxcitenames=2,mincitenames=1,giveninits=true,uniquename=init,
 isbn=false]biblatex

DeclareOuterCiteDelimsparencitebibopenbracketbibclosebracket

DeclareFieldFormatbbx@introcitemkbibbrackets#1


DeclareDelimFormatfinalnamedelimaddspace&space
DeclareDelimFormat[bib]finalnamedelim%
 ifnumgreatervalueliststop2finalandcomma%
 addspacebibstringandspace

addbibresourcebiblatex-examples.bib

begindocument
autocitecompanion,sigfridsson,worman

printbibliography
enddocument

could be a start.

The 'two-column' layout of the alphabetic style that automatically allocates enough space for each label to not run into the entry data may seem preferable, but if you cite a work by Helena Bonham Carter and Ralph Vaughn Williams, you will soon notice that the space left for the actual entry data becomes painfully narrow and does not allow for good line breaks any more.

newcommand*ambr& didn't work for me. newrobustcmdambr& worked.

documentclassarticle
usepackage[utf8]inputenc
usepackage[english]babel
usepackagecsquotes
usepackagefilecontents
usepackage[
backend=biber,
style=alphabetic,
citestyle=alphabetic,
maxcitenames=2,
mincitenames=2,
giveninits=true,
isbn=false,
]biblatex

beginfilecontents*references.bib
@articleeinstein,
 author = "Albert Einstein and Second Author",
 title = "Zur Elektrodynamik bewegter K"orper. (German)
 [On the electrodynamics of moving bodies]",
 journal = "Annalen der Physik",
 volume = "322",
 number = "10",
 pages = "891--921",
 year = "1905",
 DOI = "http://dx.doi.org/10.1002/andp.19053221004",
 keywords = "physics"


@bookdirac,
 title=The Principles of Quantum Mechanics,
 author=Paul Adrien Maurice Dirac,
 isbn=9780198520115,
 series=International series of monographs on physics,
 year=1981,
 publisher=Clarendon Press,
 keywords = physics


@booklatexcompanion,
 author = "Michel Goossens and Frank Mittelbach and Alexander Samarin",
 title = "The LaTeX Companion",
 year = "1993",
 publisher = "Addison-Wesley",
 address = "Reading, Massachusetts",
 keywords = "latex"

endfilecontents*



renewcommand*labelalphaothers$^+$
%newcommand*ambr&
newrobustcmdambr&
DeclareLabelalphaTemplate
 labelelement
 field[final]shorthand
 fieldlabel
 field[names=2, namessep=addspaceambraddspace]labelname
 
 labelelement
 literaladdspace
 
 labelelement
 field[strside=right,strwidth=2]year
 


addbibresourcereferences.bib

begindocument
sectionFirst section

Items that are cited: textitThe LaTeX Companion book citelatexcompanion, The Einstein's journal paper citeeinstein and the Dirac's book citedirac are physics related items. Next, a citation about textitThe LaTeX Companion book citelatexcompanion.

medskip

printbibliography
enddocument