[NTG-context] conditionals for font features

[Pablo Rodriguez]

Dear list,

I wonder whether there is a conditional for font features similar to
\doifelseitalic.

\doifelsecurrentfonthasfeature checks whether the font supports an
OpenType feature.

\doifunknownfontfeature checks whether the font feature has been defined.

It seems that \doifelsefontfeature checks whether the font feature has
been defined or not.

Could anyone explain me how to check whether c2sc is being used or not
in the following sample?

  \definefontfeature[asc][c2sc=yes, smcp=yes]
  \setupbodyfont[palatino]
  \starttext
  \feature[+][asc] abc\\
  \feature[-][asc] abc
  \stoptext

Many thanks for your help,

Pablo