Please allow me to ask in this thread something slightly off-topic:
why doesn't ConTeXt give a compilation error or alike when
encountering such kind of mistakes? Is it technically difficult, or
is it conventional for *TeX processors to be over tolerant?

On Sun, Feb 9, 2020 at 11:05 PM Wolfgang Schuster <
wolfgang.schuster.lists@gmail.com> wrote:

> On Mon, 10 Feb 2020 05:58:50 +0800
> Jon Wong <jhannwong@gmail.com> wrote:
>
> > MWE:
> >
> > \starttext
> >
> > The famous result (and again) is given by
> > \placeformula[formulalabel]
> > \startformula
> > c^2 = a^2 + b^2.
> > \stopformula
> > And now we can refer to formula \ref[][formulalabel].
> >
> > \stoptext
> >
> > There is a blank where the formula label should be at “now we can refer
> to formula ---“.
>
> Use \ref[number][formulalabel] or \in[formulalabel].
>
> Wolfgang
>
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