[Tex/LaTex] Biblatex ‘alphabetic’ style ‘+’ sign in citation key

Question

I noticed a strange citation key in my document. All citation keys with multiple authors are generated like this for example: [Ber+07]
Where does this + sign come from? I setup biblatex like so:

\usepackage[
   backend=biber,
   maxcitenames=3,
   maxbibnames=3,
   style=alphabetic,
   sorting=nyt]{biblatex}
\DefineBibliographyStrings{ngerman}{ 
    andothers = {{et\,al\adddot}},             
}

Do I have to write my own biblatex style?

Answer 1

The "+" is just a signal that the list of authors/editors has been truncated to fit into maxalphanames (the default value is 3), it works just like "et al." (and maxcitenames) in other styles.

Uthor et al. 2006; Uthor and Riter 2006

would be

Uth+06; UR06

The exact symbol is controlled with \labelalphaothers, so you could say

\renewcommand*{\labelalphaothers}{\&al}

to get

Uth&al06

instead.

You can increase maxalphanames to a higher value if you don't want your list truncated.