\starttext

    \definemetafont[demo-symbols][demo-symbols.mp]

    \startbuffer
        watch this: {\demo\char"261A} \quad  \ruledhbox{\demo\char"261A}
    \stopbuffer

    \definefont[demo][demo@demo-symbols]

    \getbuffer \blank

    \definefont[demo][demo@demo-symbols at \the\dimexpr3\exheight]

    \getbuffer \blank

    \definefont[demo][demo@demo-symbols at \the\dimexpr4\exheight]

    \getbuffer \blank

\stoptext