\placenamedformula{Second listed Formula}{b}
\startformula a = 3 \stopformula \endgraf
</context>
= Shaded background for part of a displayed equation =
(see also [[Framed]])
To highlight part of a formula, you can give it a gray background using <cmd>mframed</cmd>:
<context source="yes">
\setupcolors[state=start]
\def\graymath{\mframed[frame=off,
background=color,
backgroundcolor=gray,
backgroundoffset=3pt]}
\startformula
\ln (1+x) =\, \graymath{x - {x^2\over2}} \,+ {x^3\over3}-\cdots.
\stopformula
</context>