Who about something like (pseudocode)
\definecharacterkerning[letterspace]
\def\letterspace {\bgroup \dosingleempty\doletterspace}
\def\doletterspace[#1]#2% use \groupedcommand? {\iffirstargument \setupcharacterkerning[letterspace][factor=\ctxlua{tex.sprint(#1/1000)}]}%
\fi \setcharacterkerning[letterspace]#2% \egroup}
\starttext
text \letterspace{text} text \letterspace[200]{text} text looks ok, apart from the name ... we don't space letters but characters (or glyphs) so maybe \kerncharacters or so to be more concrete i think about this (why is the last value taken for
Am 25.03.10 16:21, schrieb Hans Hagen: the complete paragraph?) \definecharacterkerning[kerncharacters] \unexpanded\def\kerncharacters {\dosingleempty\dokerncharacters} \def\dokerncharacters[#1]% {\groupedcommand {\iffirstargument \setupcharacterkerning[kerncharacters][factor=\ctxlua{tex.write(#1/1000)}]% \fi \setcharacterkerning[kerncharacters]} {}} \setuphead[section][style=\sca,textstyle={\kerncharacters[250]}] \starttext \section{Section} text \kerncharacters{text} text \kerncharacters[200]{text} text \kerncharacters[2000]{text} text text {\kerncharacters text} text {\kerncharacters[200] text} text {\kerncharacters[2000] text} text text \kerncharacters[200]{text} text \kerncharacters[1000]{text} text text \kerncharacters[1000]{text} text \kerncharacters[200]{text} text \stoptext Wolfgang