On 2014–01–09 Jean-Guillaume wrote:

>  \starttext
>  \definehead[Exercise][subsection]
>  \setuphead
>     [Exercise]
>     [after=]
> \startExercise[]{(this is the exercise's title)}
> The exercise's content.
> \stopExercise
> \stoptext

\definehead
  [Exercise] [subsection]
  [after=]

\starttext
  \startExercise [title=This is the exercise's title]
    The exercise's content.
  \stopExercise
\stoptext

Marco