Using \DefineBibliographyStrings (getting undefined)?

Question

If I try to compile this MWE:

\documentclass{article}
\usepackage{biblatex}
\DefineBibliographyStrings{english}{%
  teststring      = {Test string},
}
\begin{document}
\parbox{2pt}{\hspace*{1pt}Testing my statement}
\end{document}

... it fails with:

! Package keyval Error: teststring undefined.

See the keyval package documentation for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.6 \begin{document}

Why? I'd think that \DefineBibliographyStrings would, well, define teststring? What am I doing wrong?

Answer 1

\DefineBibliographyStrings stores definitions for known strings for a language. If you want to declare a completly new string you must declare it first:

\documentclass{article}
\usepackage{biblatex}
\NewBibliographyString{teststring}
\DefineBibliographyStrings{english}{%
  teststring      = {Test string},
}
\begin{document}
\parbox{2pt}{\hspace*{1pt}Testing my statement}
\end{document}