无法为 pgfkey 设置默认值、初始值或第一个值

Question

\documentclass{article}
\usepackage{tikz}
%\pgfkeys{/tikz/scale/.show code}

\pgfkeys{tikz/.cd,
    scale/.append code={\pgfgettransformentries\scale\ab\ba\bb\xhsift\yshift},
    %scale/.initial=1, %bad
    %scale/.default=1, %bad
    %scale = 1,  %bad
}

%\tikzset{/tikz/scale=1} % bad

\begin{document}
% doesn't work
%\begin{tikzpicture}
%   \node {*\scale*} ;
%\end{tikzpicture}

% work
\begin{tikzpicture}
\pgfkeys{/tikz/scale = 2}
    \node {*\scale*} ;
\end{tikzpicture}
\end{document}