Hi Hans,

That’s wonderful! Indeed this is very handy and I’ll add it to the wiki.

However, before doing so, I would like to ask how is it possible to get the command act entirely in math mode, that is respecting the distances and the math fonts. Please see the attached output. 

%%% begin interior-of-a-set.tex
\definemathstackers[symbol][voffset=-.30\mathexheight,hoffset=\zeropoint]
\definemathover[symbol][interiorset]["2218]
\starttext

Here is the new command \type{\interiorset{K}}: $\mathring{K} \neq \interiorset{K}$

\stoptext
%%% end interior-of-a-set.tex

Best regards: OK