I want to use a dedicated font size for the chapter title, so I wrote this piece of code: %%%%%%%%%%%%%%%%%% \def\mybig% {\dosingleempty\dosanhao} \def\dosanhao[#1]% {\switchtobodyfont[24pt]} \setuphead [chapter] [style=\mybig] \starttext \chapter{hello, world} \stoptext %%%%%%%%%%%%%%%%% However, the error is: %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% ! Use of \dosanhao doesn't match its definition. \doifnextcharelse ...token =#1\def \!!stringa {#2} \def \!!stringb {#3}\futur... \@@kochapterstyle ->\mybig \bf \doconvertfont #1->\edef \p!defined {#1 }\ifx \p!defined \empty \else \@EA \d... \dosetfontattribute ...me #1#2\@EA \endcsname \fi \empty \doplaceheadnumbertext ...bute {\??ko #1}\c!style \dosetcolorattribute {\??k... \dodododoconstructhead ...{\finalsectionnumber }}} \writesection {#1}{#3}{#4}... l.11 \chapter{hello, world} %%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%% If I replace the \mybig with \switchtobodyfont in style=xx, it works fine. What's the difference between them? and why the former does not work? -- ruini