This thread brings up something that I have been thinking of for a while. Similar problems occur in amsmath aligned family which accepts an optional argument. mathtools.sty has an option so that the optional argument will work only if placed on the same line. In terms of ConTeXt that means,
\startformula[9pt] math \stopformula
\startformula [9pt] math \stopformula
will put the formula in 9pt font, while \startformula [9pt] math \stopformula
will display "[9pt] math". I have not looked into the details of how mathtools implements this, but it should be possible to port it to context. Will something like this be useful to have, or is adding \relax once in a while alright?
I guess it'll depend on how hard this is to implement. At the moment I'm dealing with lots of Lie brackets so I'd certainly appreciate this feature very much ... in my opinion it would also improve consistency: the same markup works for any kind of formula! On the other hand one could also enforce the use of \[ whenever the glyph [ should be actually typeset. This would be the other road to consistency ;-) Oliver