Hello,

       I am using Context Mark II + XeTeX. I would like to know the
following things.

1. How to use opentype font features. I tried the following code but it is
not working.
      \definefontfeature[myfontfea][+onum]
  \definetypeface[Libertine][rm][Xserif][Linux Libertine
O][default][features=myfontfea]
  \setupbodyfont[Libertine,12pt]

2. Is there an eqivalent code to the following XeLaTeX code.
      \defaultfontfeatures{Scale=MatchLowercase}

3. How to use Cambria Math font to typeset math.