\definetypeface [e] [mm] [math] [euler] [euler] [encoding=ec]
\setupbodyfont[e,10pt]
\starttext

\startbuffer
\startmathcollection[euler:texnansi]
    \definemathsymbol [breve] [accent] [tf] ["15]
\stopmathcollection
\startmathcollection[euler:ec]
    \definemathsymbol [breve] [accent] [tf] ["08]
\stopmathcollection

$\breve e$
\stopbuffer

Testing for code in \filename{cont-new.tex}
\start
  \getbuffer\typebuffer 
\stop

\startbuffer
\unprotect

 \def\dohandlemathtoken#1%
   {\csname
      \ifmmode
        \ifcsname\@mt@\outerencoding#1\endcsname
          \@mt@\outerencoding
        \else\ifcsname\@mt@\mathcollection#1\endcsname
          \@mt@\mathcollection
        \else\ifcsname\@mt@\nomathcollection#1\endcsname
          \@mt@\nomathcollection
        \else\ifcsname\characterencoding#1\endcsname
          \characterencoding
        \else
          \nocharacterencoding
        \fi\fi\fi\fi
      \else
        \ifcsname\characterencoding#1\endcsname
          \characterencoding
        \else\ifcsname\nocharacterencoding#1\endcsname
          \nocharacterencoding
        \else\ifcsname\@mt@\outerencoding#1\endcsname
          \@mt@\outerencoding
        \else\ifcsname\@mt@\mathcollection#1\endcsname
          \strippedcsname\mathematics
 \expandafter\endcsname\csname\@mt@\mathcollection
        \else\ifcsname\@mt@\nomathcollection#1\endcsname
          \strippedcsname\mathematics
 \expandafter\endcsname\csname\@mt@\nomathcollection
        \else
          \nocharacterencoding
        \fi\fi\fi\fi\fi
      \fi
    #1\endcsname}
 \let\dohandlecommand\dohandlemathtoken

 \def\checkoutermathencoding
   {\ifx\outerencoding\empty
      \ifx\outerencoding\s!default\else
        \edef\outerencoding{\currentencoding}%
      \fi
    \fi}

 \startmathcollection[texnansi]
     \definemathsymbol [breve] [accent] [tf] ["15]
 \stopmathcollection
 \startmathcollection[ec]
     \definemathsymbol [breve] [accent] [tf] ["08]
 \stopmathcollection

 \prependtoks
    \checkoutermathencoding
 \to \everymathematics

 \let\outerencoding\empty

 $\breve e$
\stopbuffer

\page

Testing for code sent by Hans on the mailing list
\start
  \getbuffer\typebuffer 
\stop



\stoptext