\showmathfontcharacters
\stoptext
When that macro is defined in s-mat-10.mkiv as
\unexpanded\def\showmathfontcharacters
{\dodoubleempty\doshowmathfontcharacters}
ConTeXt ver: 2013.04.16 12:08 MKIV beta fmt: 2013.4.19 int: english/english
! Undefined control sequence.
9 >> \showmathfontcharacters
Hans van der Meer