Pass key value pair as value with pgfkeys

Question

I want to pass a key=value pair as the value of another key=value pair. The problem is, that the equal sign gets interpreted by pgfkeys and thus I need to encapsulate it using curly brackets, which in turn prevent pgfkeys to interpret the equal sign (surprise).

The following minimal example doesn't make sense, but it illustrates what I'm trying to do. In reality I try to pass on the key=value pair to another command, which takes key=value pairs.

\documentclass[a4paper]{scrartcl}

\usepackage[utf8]{inputenc}
\usepackage{pgfkeys}

\begin{document}

\newcommand{\mycmd}[1]{%
    \pgfkeys{/mykey/.initial=hello}%
    \pgfkeys{/mykey2/.initial=world}%
    \pgfkeys{#1}%
    \pgfkeys{\pgfkeysvalueof{/mykey2}}%
    \pgfkeysvalueof{/mykey}%
    \pgfkeysvalueof{/mykey2}%
}

\mycmd{mykey2={mykey=test}}.

\end{document}

The error I get is of course: "I do not know the key '\mykey=test' ...". How can I solve this?

Edit:

Thanks to percusse I now use a style for what I'm doing. In the example below mycmdA gives the error 'I do not know the key '/fill/', while mycmdB works. Does anybody know why?

\documentclass[a4paper]{scrartcl}

\usepackage[utf8]{inputenc}
\usepackage{pgfkeys}

\begin{document}

This is a test

\newcommand{\mycmdA}[1]{%
    \pgfkeys{/mystyle/.style={##1}}%
    \pgfkeys{#1}%
}

\newcommand{\mycmdB}[1]{%
    \pgfkeys{/mystyle/.style={}}%
    \pgfkeys{/mystyle/.code=\pgfkeys{/style/.style={##1}}}
    \pgfkeys{#1}%
}

\mycmdA{mystyle={fill=red}}
\mycmdB{mystyle={fill=red}}

\end{document}

Answer 1

You don't need to reinvent the wheel. Use pgfkeys machinery for /.style and /.code handlers just as in the TikZ pictures. If mykey2 is going to be a key setter then it wouldn't be fun to also have a value. That part of the key mechanism is fairly nontrivial. But this will print test (expansion is not necessary here but just in case you need it)

\pgfkeys{mykey/.initial=hello}%
%\pgfkeys{mykey2/.initial=world}%
\pgfkeys{mykey2/.code={\expandafter\pgfkeys\expandafter{#1}}}% Expand once to remove braces
\pgfkeys{mykey2={mykey=test}}%
\pgfkeysvalueof{/mykey}%

you can instead make mykey2 a /.style and pass options to it as a key holder. Then whenever you execute mykey2 it will execute all of the stored key values (/.append style is needed for adding without resetting).