pgfdeclareshape compilation error

Question

Starting from a more complex trial to add a new shape, I arrive to this minimal example which does not compile. I use PGF 2.10

\documentclass[12pt]{article}

\usepackage{tikz}
\pgfdeclareshape{minex}{}
\begin{document}
\begin{tikzpicture}
\node[minex] {};
\end{tikzpicture}
\end{document}

The received error message is :

ERROR: Package PGF Math Error: Unknown function `center' (in 'center').

TeX said:

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

l.7 \node[minex] {};

Answer 1

Define at least a center anchor, then the error goes away:

\pgfdeclareshape{minex}{\anchor{center}{\pgfpointorigin}}

Answer 2

Add some definitions (inherited or not) :

\documentclass[12pt]{article}

\usepackage{tikz}
\pgfdeclareshape{minex}{
  \inheritsavedanchors[from=rectangle]
  \inheritanchorborder[from=rectangle]
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{north}
  \inheritanchor[from=rectangle]{south}
  \inheritanchor[from=rectangle]{west}
  \inheritanchor[from=rectangle]{east}
  \inheritanchor[from=rectangle]{north west}
  \inheritanchor[from=rectangle]{south east}
  \inheritanchor[from=rectangle]{south west}
  \inheritanchor[from=rectangle]{north east}
  \inheritanchor[from=rectangle]{center}
  \inheritanchor[from=rectangle]{base}
  \inheritanchor[from=rectangle]{base east}
  \inheritanchor[from=rectangle]{base west}
  \inheritanchor[from=rectangle]{mid}
  \inheritanchor[from=rectangle]{mid east}
  \inheritanchor[from=rectangle]{mid west}
  %....
}   
\begin{document}
\begin{tikzpicture}
\node[shape=minex] {};
\end{tikzpicture}
\end{document}