Why do I get an error on

\starttext

\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