%font size
\setuppagenumbering[state=stop, way=bytext]
\enableregime[utf]
\setupbodyfont[12pt]

\starttext
Normal size font\par
{\tfxx decrease the font size by two}\par
{\tfa increase font size by one}\par
{\bfa increase font size by one and make bold}\par
{\tfb increase font size by two}\par
{\ssd create a sans serif font and increase its size by four}\par


\stoptext
