50 关于NewExpandableDocumentCommand的展开问题？

在链接A中，Eureka老师给了一个例子：

\documentclass[border=6pt]{standalone}
\usepackage{tikz}
\NewExpandableDocumentCommand\testB{m}{color = #1}
\NewExpandableDocumentCommand\testC{m}{#1}
\begin{document}
\begin{tikzpicture}
    \draw[\testB{magenta}] (0,0)--(1,1);  % failed
    \draw[\testC{cyan}] (0,0)--(1,0);  % works
\end{tikzpicture}
\end{document}

\draw[\testB{magenta}] (0,0)--(1,1); 因为展开顺序问题报错
\draw[\testC{cyan}] (0,0)--(1,0); 因为省略了color=而可以正常运行

但在链接B中类似的\inns却不可行。

\documentclass{article}
\usepackage{tikz}
\begin{document}
\NewExpandableDocumentCommand\inns{m}{inner sep=#1 pt}
\tikz{
    \node(a) at (0,0) {A};
    % \node[\inns{2}] (b) at (1,0) {B}; % fails
    \node[/tikz/inner sep=2pt] (b) at (1,0) {B}; % works
    \node[/pgf/inner sep=2pt] (b) at (1,0) {B}; % works
    \node[inner sep=2pt] (b) at(1,0) {B}; % works
    \expanded{\noexpand\node[\inns{2}]}(b)at(1,0){B}; % works
    \expandafter\node\expanded{[\inns{2}]}(b)at(1,0){B}; % works
    \draw(a) -- (b);
}
\end{document}

其中\node[\inns{2}] (b) at (1,0) {B};提示信息为：

Package pgfkeys: I do not know the key '/tikz/inner sep=2 pt' and I am going to ignore it. Perhaps you misspelled it.

这提示\inns已经被展开为inner sep=2 pt了，而且根据文档，句柄/tikz/inner sep与/pgf/inner sep实际是等价的，这令人非常不解。求解释~

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