colnames.tex

\documentclass[12pt]{scrartcl}
\usepackage{pgfkeys}

\newcommand\colnames

\pgfkeys
{
  /foo/.is family, /foo,
  default/.style =
  {
    colnames,
  },
  colnames/.estore in = \colnames,
  colnames/.default = {},
}
\begin{document}

\NewDocumentCommand{\fee}{O{}}
{
  \pgfkeys{/foo, default, #1}%
  \typeout{FEE RETURNS \colnames}\colnames
}

\fee[colnames={[[`To`]], [[`From`]]}]

\NewDocumentCommand{\baz}{m}{\typeout{BAZ REURNS #1}#1}

\baz{{[[`To`]], [[`From`]]}}

\end{document}

%%% Local Variables:
%%% mode: latex
%%% TeX-master: t
%%% End: