On 2013–08–26 Hans Hagen wrote:

> not a bug ... just not implemented (as it's pretty complex to do
> that case efficiently at the tex end)
> 
> anyhow, as it seems to be needed, i redid the code and now we have:
> 
> […]
> 
> so, three optional qualifiers (also in that order), so you'd better
> wikify it

  http://wiki.contextgarden.net/starttexdefinition

Thanks for the implementation.

Marco