TikZ scope arrow style: not used for complex style?

Question

I would like to use the double -latex arrow style in a whole scope.

When I define a simple style myarrow plain which only sets red color the scope style is applied in \begin{scope}[myarrow plain] \draw ... \end{scope} and I don't have to say \draw[myarrow plain]: plain explicit and plain scope in the image.

For myarrow complex style, which entails double -latex, the scope only changes foreground color (complex scope below) and I have to say \draw[myarrow complex] to have the double arrow (complex explicit).

Can I get an explanation how to declare the myarrow complex style correcetly so that the scope uses it? I am guessing it has to do with postaction, or appending vs. defining to style, but I know too little about TikZ internals (so far).

\documentclass[margin=2mm]{standalone}
\usepackage{tikz} 
\usetikzlibrary{arrows}
% https://tex.stackexchange.com/a/72793
\tikzset{
  double -latex/.style args={#1 colored by #2 and #3}{    
    -latex,line width=#1,#2,
    postaction={draw,-latex,#3,line width=(#1)/3,shorten <=(#1)/4,shorten >=4.5*(#1)/3},
  }
}
\tikzset{
    myarrow complex/.style={line width=2mm,double -latex=2mm colored by brown and red},
    myarrow plain/.style={-latex,color=red}
}
\begin{document}
\begin{tikzpicture}
    \begin{scope}[myarrow complex]
        \draw (0,1) to node[pos=.5,below]{complex scope} (4,1);
        \draw[myarrow complex] (0,0) to node[pos=.5,below]{complex explicit} (4,0);
    \end{scope}
    \begin{scope}[myarrow plain]
        \draw[myarrow plain] (0,3) to node[pos=.5,below]{plain explicit} (4,3);
        \draw (0,2) to node[pos=.5,below]{plain scope} (4,2);
    \end{scope}
\end{tikzpicture}
\end{document}

Answer 1

P. 187 in the manual about preaction and postaction

...this option only has an effect when given to a \path or as part of the options of a node; as an option to a {scope} it has no effect.

If you want the postaction to be applied to every path in the scope, you can use every path/.style. To stop a recursive runaway. you can use nomorepostaction from

https://tex.stackexchange.com/a/5354/8650

like this:

\documentclass[tikz, border=1cm]{standalone}
\makeatletter
\tikzset{nomorepostaction/.code=\let\tikz@postactions\pgfutil@empty}
\makeatother
\tikzset{
double -latex/.style args={#1 colored by #2 and #3}{    
-latex, line width=#1, #2,
every path/.style={postaction={nomorepostaction, draw, -latex, #3, line width=(#1)/3, shorten <=(#1)/4, shorten >=4.5*(#1)/3}}
}}
\tikzset{
myarrow complex/.style={line width=2mm, double -latex=2mm colored by brown and red},
myarrow plain/.style={-latex, color=red}
}
\begin{document}
\begin{tikzpicture}
\begin{scope}[myarrow complex]
\draw (0,1) to node[pos=.5, below]{complex scope} (4,1);
\draw[myarrow complex] (0,0) to node[pos=.5, below]{complex explicit} (4,0);
\end{scope}
\end{tikzpicture}
\end{document}