Changes
commented code. Took me forever to wrap my head around.
\definesystemvariable {dt} % DocumentTitle
% Expand both 1- and 2- arity'd versions of /dosetuptitle
\def\setuptitle
{\dodoubleempty\dosetuptitle}
% The one-argument iteration:
% For each comma separated item of arg1, define (dtcontent(arg1))...
% using \setuptitle in your document as defined at the bottom of this file
% The two-argument iteration:
% For each comma separated item of arg1, and using style/color in arg2...
% define (dt(arg1)(style)) and (dt(arg1)(color))
\def\dosetuptitle[#1][#2]%
\processcommalist[#1]\dododosetuptitle}
% Using earlier style/color definitions, apply style and color to arg1-item values
\def\placetitle
{\startalignment[\v!middle]
\stopalignment}
% Here is where we define the key-value pairs
\setuptitle
[\c!title]