\environment xits-env

\startbuffer[Alpha]
  ABCDEFGHIJKLMOPQRSTUVWXYZ
\stopbuffer

\startbuffer[alpha]
  abcdefghijklmopqrstuvwxyz
\stopbuffer

\starttext

\startformula
  \startalign[align=middle]
    \mathcal{\getbuffer[Alpha]}\NR
    \mathcal{\getbuffer[alpha]}\NR
  \stopalign
\stopformula

\stoptext